GIFT   OF 
Publisher 


fcDUCATJON  DEFT, 


A  LABORATORY   COURSE   IN   PHYSICS 
OF   THE   HOUSEHOLD 


THE  MACMILLAN  COMPANY 

NEW  YORK   •    BOSTON   •    CHICAGO  •    DALLAS 
ATLANTA  •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON   •    BOMBAY  •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


A  LABORATORY  COURSE/ 

IN 

PHYSICS  OF  THE  HOUSEHOLD 

TO  ACCOMPANY 

LYNDE'S   PHYSICS   OF  THE  HOUSEHOLD 


BY 


CARLETON  JOHN  LYNDE,  PH.D. 

PROFESSOR  OF  PHYSICS  IN  MACDONALD  COLLEGE 
CANADA 


Nefo 

THE  MACMILLAN  COMPANY 
1922 

All  rights  reserved 


^2*    .-. 


COPYRIGHT,  1919, 
Bv  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotypcd.     Published  March,  1919, 


eDUCATIQN  DEPT. 


NortnoolJ 

J.  S.  Cashing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THIS  Laboratory  Course  in  Physics  of  the  Household  covers 
the  ground  recommended  by  the  College  Entrance  Board.  It 
differs  from  similar  courses  in  four  ways :  first,  it  contains  Exercises 
in  addition  to  the  usual  Experiments ;  second,  it  requires  the  use 
of  the  common  weights  and  measures  side  by  side  with  the  metric 
weights  and  measures ;  third,  it  permits  the  use  of  much  apparatus 
familiar  to  the  student;  and  fourth,  it  encourages  the  student 
to  set  up  a  laboratory  in  his  own  home. 

The  Exercises  help  the  student  to  appreciate  how  physics  is 
applied  in  his  home  and  in  his  environment  in  general.  The 
Exercises  and  Experiments  together  complement  the  classroom 
work. 

The  use  of  the  common  weights  and  measures  in  addition  to 
the  metric  weights  and  measures  is  justified,  in  the  writer's  opinion, 
as  follows.  Since  we  require  young  students  to  take  a  laboratory 
course  in  physics  in  order  that  they  may  obtain  knowledge  which 
they  will  apply  in  everyday  life,  it  seems  wise  to  allow  them  to 
obtain  this  knowledge  in  terms  of  the  units  (foot,  pound,  B.T.U., 
etc.)  which  they  must  use  when  they  so  apply  it.  Furthermore, 
the  writer,  although  a  strong  advocate  of  the  metric  system,  be- 
lieves that  it  is  pedagogically  unsound  to  try  to  teach  physics  by 
means  of  the  metric  system  exclusively.  It  is  an  attempt  to  teach 
an  unknown  subject  by  means  of  an  unknown  system  of  weights 
and  measures  and  it  leads  to  confusion  and  lack  of  power  on  the 
part  of  the  student.  Long  experience  leads  the  writer  to  believe 
that  the  correct  method  is  to  introduce  the  subject  by  means  of 
the  common  system  and  then  to  use  the  two  systems  side  by  side. 
This  is  the  method  followed  in  this  book. 


vi  PREFACE 

There  are  three  reasons  why  familiar  apparatus  (3-qt.  pail, 
spring  balance,  common  thermometer,  etc.)  is  used.  If  the  student 
uses  apparatus  with  which  he  is  familiar,  he  finds  that  he  can  make 
experiments  at  home  and  he  learns  that  an  experiment  may  be 
made  when  and  where  information  is  desired ;  whereas,  if  he  uses 
only  the  apparatus  commonly  found  in  a  school,  he  is  likely  to  get 
the  impression  that  an  experiment  is  something  to  be  made  only 
in  the  school  laboratory.  The  familiar  apparatus,  moreover, 
allows  a  student  to  work  with  large  quantities  and  thereby  decreases 
the  chances  of  error.  Also  the  familiar  apparatus  is  cheap  and 
easy  to  obtain. 

The  reason  for  encouraging  the  student  to  set  up  a  laboratory 
at  home  is  obvious.  If  he  plans  his  own  experiments  on  a  given 
subject  and  then  makes  these  experiments,  he  gets  a  firmer  grasp 
of  the  subject  than  if  he  makes  only  the  experiments  in  school. 

The  apparatus  required  for  these  experiments  (except  for  a  few 
in  electricity)  is  simple  and  inexpensive  and  much  of  it  is  similar 
to  that  now  found  in  high  school  laboratories.  It  is  advisable  to 
have  one  set  for  each  two  students  in  order  that  the  whole  class 
may  make  the  same  experiment  at  the  same  time.  Where  only 
one  or  two  sets  can  be  purchased,  however,  the  class  may  make 
the  experiments  in  rotation. 

For  the  convenience  of  those  ordering  apparatus,  we  give  on 
pages  139-146  a  list  of  the  apparatus  required,  with  the  approximate 
cost,  and  also  the  names  and  addresses  of  a  number  of  firms  from 
which  the  apparatus  may  be  purchased.  The  prices  quoted  are 
those  in  effect  before  the  war.  The  present  prices  can  be  obtained 
by  writing  to  any  of  the  firms  mentioned. 

C.  J. L. 


CONTENTS 

PAGE 

Introduction  to  the  Students :   APPARATUS  FOR  A  HOME  LABORATORY    xi-xv 

MECHANICS 

EXPERIMENT 

1.  LEVERS  OF  THE  FIRST  CLASS i 

2.  LEVERS  OF  THE  SECOND  AND  THIRD  CLASS 4 

Exercise    i.   Lever  Appliances 7 

3.  PULLEYS 9 

Exercise    2.   Pulley  and  Screw  Appliances 12 

4.  COMMON  WEIGHTS  AND  MEASURES  .......  13 

5.  METRIC  WEIGHTS  AND  MEASURES 14 

Exercise    3.    Kitchen  Measuring  Appliances      .         .        .  •      .        .  15 

Exercise    4.   Water  Supply        .........  16 

Exercise    5.   Water  Supply  Plumbing        .        .        .        .        .        .  16 

Exercise    6.   Sewage  Plumbing 16 

6.  LAW  OF  ARCHIMEDES         .        .        . 17 

7.  VOLUME  AND  DENSITY      ....        .        .        .        .        .  19 

8.  DENSITY  OF  SOLIDS  . .     .  22 

9.  DENSITY  OF  LIQUIDS         .        .        . 24 

Exercise    7.    Gas  Plumbing 25 

10.  BAROMETER  AND  SIPHON 26 

Exercise    8.   Plumbing  Traps     .                 28 

11.  BOYLE'S  LAW 29 

Exercise    9.   Fire  Extinguishers          .        .        ...        .        .31 

Exercise  10.   Vacuum  Cleaner 31 

HEAT 

12.  THERMOMETERS 33 

Exercise  ii.  Thermometers .        .34 

13.  EXPANSION  OF  BRASS .  35 

vii 


viii  CONTENTS 

EXPERIMENT  PAGE 

14.  EXPANSION  OF  AIR    .        .        .        .        .        .        ,        .        .        .37 

Exercise  12.    Kitchen  Range      .        .         .        .         .         .         .         .38 

Exercise  13.   Heating  System 39 

Exercise  14.   Hot  Water  Boiler 39 

15.  How  TO  MEASURE  HEAT 40 

Exercise  15.    Cooking  Utensils   .         .        .        .         .         .        .         .42 

Exercise  16.    Fireless  Cooker      .        .        .        '.        .        .        .        .      43 

Exercise  17.   Thermos  Bottle     .        .        .        .        .      •'.'...        .      44 

Exercise  18.   Ventilation    .         .  ....         .         .         .       44 

16.  COOLING  EFFECT  OF  ICE  AND  OF  ICE  WATER.        .        .        .        .      45 

17.  HEATING  EFFECT  OF  STEAM  AND  OF  BOILING  WATER     ...      47 

18.  SPECIFIC  HEAT  .  .        .        .        .        .        .        .        .        .49 

19.  LATENT  HEAT  OF  FUSION  OF  ICE     . 54 

Exercise  19.   Refrigerators          .        .         .        .        .        .        .        -57 

Exercise  20.   Artificial  Refrigeration  .        .        '..-..'".        .        .       57 

20.  LATENT  HEAT  OF  STEAM ,        ...      58 

Exercise  21.   Fuels  .        .        .        .        .      62 


ELECTRICITY  AND  MAGNETISM 

21.  THE  SIMPLE  CELL     .   ' .        .64 

22.  MAGNETS  . •,        .        .        .      67 

23.  MAGNETIC  FIELDS     .        .        .        .        .        .       .    -    .        .        .      70 

24.  MAGNETIC  EFFECT  OF  AN  ELECTRIC  CURRENT        .        .        .        .      72 

25.  APPLICATIONS  OF  THE  ELECTROMAGNET    .        .        .        .        ...     .      77 

Exercise  22.   Bell  Circuit    .        .         .        ...        .        .        .78 

26.  ELECTRIC  MOTOR .        .  -79 

Exercise  23.    Electric  Motors     .         .        .        ......         .81 

Exercise  24.    Electric  Heating  and  Cooking  Appliances      .         .         .82 
Exercise  25.   Electric  Lighting 82 

27.  ELECTROLYSIS,  ELECTROPLATING  AND  THE  STORAGE  CELL       .        .      84 

28.  MEASUREMENT  OF  RESISTANCE         .......      87 

29.  RESISTANCE  MEASURED  BY  VOLTMETER-AMMETER  METHOD     .        .      89 

30.  CELLS  CONNECTED  IN  SERIES  AND  IN  PARALLEL     ....      92 

31.  INDUCED  CURRENTS  ,,,,,,        f       ,       ,       .      93 


CONTENTS  IX 

EXPERIMENT  PAGE 

32.  APPLICATIONS  OF  INDUCED  CURRENTS      ......  96 

Exercise  26.    Electric  Light  Plant       .......  99 

Exercise  27.   Telephone  Exchange 99 

Exercise  28.   Wireless  Station 99 

33.  HORSE-POWER  AND  EFFICIENCY  OF  AN  ELECTRIC  MOTOR        .        .  100 

LIGHT 

34.  THE  PHOTOMETER      .        » 104 

Exercise  29.   Lighting         . 105 

35.  REFLECTION  OF  LIGHT       .        .        .        .        .        .        .        .        .  107 

36.  INDEX  OF  REFRACTION  OF  GLASS no 

37.  FOCAL  LENGTH  AND  CONJUGATE  Foci  OF  A  CONVERGING  LENS      .  112 

38.  SIZE  OF  REAL  IMAGE  FORMED  BY  A  CONVERGING  LENS         .        -115 

39.  MAGNIFYING  POWER  OF  A  LENS  USED  AS  A  SIMPLE  MICROSCOPE  .  116 
Exercise  30.   Light  Appliances  .         .         .         .         .         .         .  117 

40.  THE  ASTRONOMICAL  TELESCOPE 119 

41.  REFRACTION  AND  DISPERSION  OF  LIGHT  BY  A  PRISM      .        .        .121 

SOUND 

42.  VELOCITY  OF  SOUND           123 

43.  NUMBER  OF  VIBRATIONS  OF  A  TUNING  FORK  .        .        .        .        .125 

44.  WAVE  LENGTH  OF  SOUND 127 

45.  VIBRATING  STRINGS 129 

ADVANCED    MECHANICS 

46.  THE  PARALLELOGRAM  LAW 131 

47.  EFFICIENCY  OF  A  MACHINE 133 

48.  ACCELERATED  MOTION 135 

49.  LAWS  OF  THE  PENDULUM 137 

APPENDIX 

TABLE  OF  DENSITIES       .        .        .        .        .        .                 .        .        .  138 

APPARATUS  FOR  LYNDE'S  LABORATORY   COURSE  IN   PHYSICS  OF  THE 

HOUSEHOLD    ...........  139 

APPARATUS  FOR  STUDENT'S  PRIVATE  LABORATORY  .        ,        .        .        -143 


TO   THE   STUDENTS 

MANY  of  you  who  take  this  course  will  wish  you  could  make 
experiments  at  home.  To  help  you  to  do  this  we  list  on  pages 
143-145  and  illustrate  in  Figs,  i,  2,  3  and  4  below,  the  apparatus 
needed  for  a  home  laboratory.  With  this  equipment  you  can 
perform,  in  whole  or  in  part,  more  than  two  thirds  of  the  experi- 
ments outlined  in  this  book  and  many  experiments  of  your  own. 


FIG.  i.     Apparatus  for  a  student's  home  laboratory  in  Mechanics. 


The  apparatus  needed  for  a  home  laboratory  in  Mechanics  is 
illustrated  in  Fig.  i  (except  four  single  pulleys)  and  listed  on  page 


Xll 


TO  THE   STUDENTS 


143.  With  this  equipment  you  can  make,  in  whole  or  in  part, 
experiments  i,  2,  3,  4,  5,  6,  7,  8,  9,  10,  n.  You  will  need  to  find 
at  home,  some  cord,  a  piece  of  rock,  a  piece  of  iron  (an  old  flatiron 
will  do),  and  a  quart  bottle. 


FIG.  2.     Additional  apparatus  for  a  student's  laboratory  in  Heat. 

The  additional  apparatus  required  for  a  home  laboratory  in 
Heat  is  illustrated  in  Fig.  2  and  listed  on  page  144 ;  with  this  you 
can  make,  in  whole  or  in  part,  experiments  12,  14,  15,  16,  17,  18, 
19,  20.  If  gas  is  not  available,  you  can  use,  as  a  source  of  heat,  an 
alcohol  stove,  an  oil  stove,  or  the  kitchen  range. 

The  apparatus  needed  for  a  home  laboratory  in  Electricity  and 
Magnetism  is  illustrated  in  Fig.  3  and  listed  on  page  144 ;  with  this 
you  can  make,  in  whole  or  in  part,  experiments  21,  22,  23,  24,  25, 
26,  27.  You  will  need  also  the  supplies  listed  on  page  145. 

The  apparatus  for  a  home  laboratory  in  Light  and  Sound  is 
illustrated  in  Fig.  4,  and  listed  on  page  145  ;  with  this  you  can  make, 
in  whole  or  in  part,  experiments  34,  35,  36,  37,  38,  39,  40,  41,  45. 


TO  THE   STUDENTS 


xru 


•c  ] 


XIV  TO  THE   STUDENTS 

With  the  pendulum  bob  listed  on  page  145  and  with  apparatus 
listed  under  Mechanics  you  can  make  experiments  47,  48,  49,  in 
Advanced  Mechanics. 

You  will  need  at  home  a  table  on  which  to  make  the  experiments, 
and  a  towel  to  dry  the  apparatus. 


FIG.  4.     Apparatus  for  a  student's  home  laboratory  in  Light  and  Sound. 

You  will  find  that  the  most  satisfactory  way  to  make  your  own 
experiments  is  to  think  them  out  before  you  start  and  to  put  them 
down  on  paper  somewhat  as  follows : 

1.  Outline  the  experiment  you  intend  to  make. 

2.  Make  a  rough  drawing  showing  how  you  intend  to  arrange 
the  apparatus. 

3.  State  the  results  you  expect  to  obtain. 

When  you  have  planned  your  work  as  above,  make  the  experi- 
ment and  compare  the  results  you  obtain  with  those  you  expected 
to  obtain.  Follow  this  plan  with  each  experiment. 

You  will  get  a  great  deal  of  pleasure  out  of  this  work  at  home 
because  you  will  find  it  very  exhilarating  to  make  experiments  of 
your  own ;  you  will  get  a  great  deal  of  profit  also  because  when 


TO   THE   STUDENTS 


XV 


you  have  planned  and  made  experiments  of  your  own  on  a  given 
subject,  you  will  find  that  you  know  it  in  a  way  you  never  could 
simply  by  making  the  experiments  in  school. 

The  prices  quoted  are  those  in  effect  before  the  war.  You  can 
get  the  present  prices  by  writing  to  one  of  the  firms  listed  on 
page  146.  If  the  cost  is  too  great  for  one  student,  a  number 
might  club  together  to  buy  the  apparatus  or  at  least  part  of  it. 

C.  J.  L. 


A  LABORATORY  COURSE  IN  PHYSICS 
OF  THE  HOUSEHOLD 

MECHANICS 

Experiment  1.     Levers  of  the  first  class. 

To  illustrate  the  lever  law  by  means  of  a  lever  of  the  first  class. 


Yard  stick.  Two  i  Ib.  weights.1 

Support.  Meter  stick. 

One  2  Ib.  weight.1  Four  100  g.  weights. 


The  lever  law  is :  A  lever  is  balanced  when  the  total  moment  on 
one  side  of  the  fulcrum  is  equal  to  the  total  moment  on  the  other. 
The  moment  of  a  weight  is  found  by  multiplying  the  weight  by  its 
distance  from  the  fulcrum. 

Method  i.  Balance  a  yard  stick,  as  shown  in  Fig.  5,  until  it 
remains  horizontal.  Note  carefully  the  exact  position  of  the  ful- 
crum and  make  all  measurements  from  this  point. 

Make  the  four  experiments  outlined  below  and  two  or  three  of 
your  own.  In  each  case,  use  the  lever  law  to  calculate  the  distance 
you  expect  to  find.  Then  make  the  experiment  and  notice  whether 
the  distance  found  by  experiment  agrees  with  that  found  by  cal- 
culation. 

1  Convenient  weights  of  i  Ib.,  2  Ib.,  etc.,  can  be  made  by  filling  cotton  bags  with  sand 
or  shot  to  the  proper  weight. 

B  I 


LABORATORY  COURSE   IN  PHYSICS 


WEIGHT 

DISTANCE 
FROM  FULCRUM 

WEIGHT 

DISTANCE  FROM  FULCRUM 

By  calculation 

By  experiment 

ilb. 

1  6  in. 

balances 

ilb. 

ilb. 

1  6  in. 

balances 

alb. 

ilb. 

15  in. 

balances 

3lb. 

ilb. 

6  in.  j 

balance 

2lb. 

i  Ib. 

12  in.  j 

Method  2.     Balance  a  meter  stick.     Make  the  four  experiments 
outlined  below  and  two  or  three  of  your  own. 


WEIGHT 

DISTANCE  FROM 
FULCRUM 

WEIGHT 

DISTANCE  FROM  FULCRUM 

By  calculation 

By  experiment 

100  g. 

40  cm. 

balances 

100  g. 

100  g. 

40  cm. 

balances 

200  g. 

100  g. 

45  cm. 

balances 

300  g. 

100  g. 
100  g. 

20  cm.  1 
40  cm.  / 

balance 

200  g. 

Does  the  lever  law  hold  in  each  case ;  that  is,  is  the  total  moment 
on  one  side  of  the  fulcrum  always  equal  to  the  total  moment  on 
the  other  side  when  the  lever  balances? 


4  LABORATORY   COURSE   IN  PHYSICS 

Experiment  2.     Levers  of  the  second  and  third  class. 

To  illustrate  the  lever  law  by  means  of  levers  of  the  second 
and  third  class. 

Yard  stick.  One  i  Ib.  weight. 

Spring  balance  with  reading  One  2  Ib.  weight. 

in  ounces  and  grams.  Meter  stick. 

Block.  Two  100  g.  weights 

Support.  One  500  g.  weight. 

Method.     Levers   of   the   second    class,     (i)    Support   a   yard 
stick  as  shown  in  Fig.  6.     One  end,  the  fulcrum,  rests  on  a  block ; 


FIG    6.     Apparatus  used  to  illustrate  levers  of  the  second  class. 

the  other  end  is  supported  by  a  cord  attached  to  a  spring  balance 
with  a  scale,  divided  into  ounces.  In  all  cases  make  the  fulcrum 
the  end  at  which  the  numbers  on  the  yard  stick  begin. 


LABORATORY  COURSE  IN  PHYSICS 


5 


Find  the  force  recorded  on  the  balance 1  when  there  are  no  weights 
on  the  lever,  that  is,  the  force  required  to  support  one  end  of  the 
yard  stick.  Subtract  this  amount  from  all  readings  of  the  balance. 

Make  the  three  experiments  given  below  and  two  of  your  own. 
In  each  case,  use  the  lever  law  to  calculate  the  force  you  expect 
to  find.  Then  find  the  force  by  experiment. 


WEIGHT 

DISTANCE 
FROM  FUL- 
CRUM 

FORCE 

DISTANCE 
FROM  FUL- 
CRUM 

By  calculation 

By  experiment 

I  lb. 

1  8  in. 

is  balanced  by 

36  in. 

2lb. 

18  in. 

is  balanced  by 

36  in. 

3lb. 

12  in. 

is  balanced  by 

36  in. 

(2)  Support  a  meter  stick  as  shown  in  the  illustration.  Find 
the  force  in  grams  required  to  support  one  end  of  the  meter  stick 
when  there  are  no  weights  on  it.  Subtract  this  amount  from  all 
readings  of  the  balance. 

Make  the  three  experiments  given  below  and  two  of  your  own. 
In  each  case  find  the  force  in  grams,  first  by  calculation,  and  then 
by  experiment. 


WEIGHT 

DISTANCE 
FROM  FUL- 
CRUM 

FORCE 

DISTANCE 
FROM  FUL- 
CRUM 

By  calculation 

By  experiment 

200  g. 

50  cm. 

is  balanced  by 

ioo  cm. 

200  g. 

75  cm. 

is  balanced  by 

100  cm. 

500  g. 

40  cm. 

is  balanced  by 

ioo  cm. 

1  If  the  end  of  the  pointer  of  the  spring  bahnce  is  blunt,  it  is  necessary  to  find  a 
p  ;int  on  the  end  from  which  to  make  your  readings.  Do  this  as  follows  :  Suspend  the 
balance  without  weights  and  notice  the  point  opposite  the  zero  line.  Make  all  subse- 
quent readings  from  this  point. 


6  LABORATORY   COURSE  IN  PHYSICS 

Method.  Levers  of  the  third  class,  (i)  Support  a  yard  stick 
as  shown  in  Fig.  7.  One  end,  the  fulcrum,  is  held  down  by  hand ; 
the  weight  is  attached  near  the  other  end,  and  a  spring  balance 
exerts  a  force  upwards  at  some  point  between. 

NOTE.  —  Hold  the  fulcrum  down  with  one  finger  exactly  at  the  end 
of  the  lever,  but  do  not  bear  down  on  the  balance. 


I 


FIG.  7.     Apparatus  used  to  illustrate  levers  of  the  third  class. 

Find  the  force  in  ounces  required  to  support  the  yard  stick 
when  there  are  no  weights  on  it.  Subtract  this  amount  from 
all  readings  of  the  balance.  Make  the  two  experiments  given 
below  and  one  of  your  own.  In  each  case  use  the  lever  law  to 
calculate  the  force  in  ounces  you  expect  to  find,  then  find  it  by 
experiment. 


LABORATORY  COURSE  IN  PHYSICS 


DISTANCE 

FORCE 

DISTANCE 

WTTTPTTT 

CRUM 

By  calculation 

By  experiment 

CRUM 

ilb. 

36  in. 

is  balanced  by 

18  in. 

2lb. 

27  in. 

is  balanced  by 

18  in. 

(2)  Support  a  meter  stick  as  shown  in  Fig.  7.  Find  the  force 
in  grams  required  to  support  the  meter  stick  when  there  are  no 
weights  on  it.  Subtract  this  amount  from  each  reading  on  the 
balance.  Make  the  two  experiments  given  below  and  one  of  your 
own.  In  each  case,  find  the  force  in  grams,  first  by  calculation 
and  then  by  experiment. 


FORCE 

DISTANCE 

DISTANCE 

WEIGHT 

FROM 

FROM  FUL- 

FULCRUM 

By  calcula- 
tion 

By  experiment 

CRUM 

200  g. 

75  cm. 

is  balanced  by 

50  cm. 

500  g. 

80  cm. 

is  balanced  by 

50  cm. 

Does  the  lever  law  hold  in  each  case,  that  is,  is  the  total  moment 
upward  always  equal  to  the  total  moment  downward  when  the 
lever  is  balanced? 

Exercise  1.     Lever  Appliances. 

Measure  the  force  arm  and  weight  arm  of  at  least  five  of  the 
following  lever  appliances  and  calculate  the  advantage  of  each : 
tack  lifter,  scissors,  can  opener,  nutcracker,  potato  ricer,  knife, 
fork,  spoon,  broom,  fire  tongs,  sugar  tongs. 

Make  a  rough  sketch  of  each  appliance  and  mark  on  it  the  force 
arm,  weight  arm,  advantage,  and  the  lever  class  to  which  it  belongs. 


8  LABORATORY  COURSE  IN  PHYSICS 

Measure  the  force  arm  and  weight  arm  of  at  least  four  of  the 
following  wheel  and  axle  appliances :  grate  shaker,  wringer,  coffee 
mill,  ice-cream  freezer,  bread  mixer,  cake  mixer. 

Make  a  diagram  of  each  and  mark  on  it  the  force  arm,  weight 
arm,  and  advantage. 

Home  Exercise. 

Repeat  this  exercise  with  at  least  three  lever  appliances  and 
two  wheel  and  axle  appliances  in  your  home. 

Make  a  written  report  on  this  work. 


LABORATORY   COURSE  IN  PHYSICS 


Experiment  3.     Pulleys. 

To  verify  the  law  of  the  pulleys. 

Four  single  pulleys. 
Support. 

Spring  balance  (ounces  and 
grams). 


One  2  Ib.  weight. 
One  i  Ib.  weight. 
One  500  g.  weight. 
Three  100  g.  weights. 


FIG.  8. 
weight. 


(2)  (5) 

Commercial  pulleys  with  one,  two,  three,  and  four  ropes  supporting  the 


The  law  of  the  pulley  is  :  //  there  is  no  friction,  the  force  is  equal 
to  the  weight  divided  by  the  number  of  ropes  supporting  the  weight, 
The  force  mentioned  here  is  the  force  which  would  be  required  to 
support  a  given  weight,  if  the  pulleys  were  without  friction  and 
without  weight. 

Method  i.  In  all  cases,  use  the  law  of  the  pulley  to  calculate  the 
force  you  expect  to  find,  then  find  the  force  by  experiment. 

If  the  laboratory  is  equipped  with  the  common  commercial 


IO 


LABORATORY  COURSE  IN  PHYSICS 


pulleys  shown  in  Fig.  8,  use  these,  and  use  weights  ten  times  greater, 
in  each  case,  than  those  mentioned  below.  If  not,  use  small  single 
pulleys,  and  when  there  are  two  pulleys  in  a  block,  as  in  (3)  and 
_  _  (  (4)  Fig.  8,  use  two  single  pul- 

leys, one  under  the  other  for 
each  double  block,  as  shown 
in  Fig.  9. 

(1)  Arrange  a  single  pulley 
as  shown  in  (i)  Fig.  8.     Use 
a  spring  balance  to  find  the 
force  required  to  support  a 
weight  of  i  Ib. 

(2)  Arrange  two  pulleys  as 
shown  in  (2)  Fig.  8.  Find  the 
force  required  to  support  the 
lower  pulley  alone  ;  then  find 
the   extra   force    needed    to 
support  a  weigh  of  2  Ib. 

(3)  Arrange  three  pulleys 
as  shown  in  (3)  Fig.  8.     Find 
the  force  required  to  support 
the  lower  pulley  alone  ;  then 
find  the  extra  force  required 


FIG.  9.     Four   small   single  pulleys  so  ar- 
ranged  that  there  are  four  strings  supporting 

the  weight. 


to  SUppOrt  a  weight  of  3  Ib. 

/   \     »  f  n 

(4)  Arrange   four   pulleys 
as  in  Fig.  9,  or  (4)  Fig.  8. 
Find  the  force  required  to  support  the  lower  pulleys  ;    then  find 
the  extra  force  required  to  support  a  weight  of  2  Ib. 
(5)  and  (6)  Make  two  experiments  of  your  own. 

NOTE.  —  The  friction  in  the  pulley  bearings  opposes  any  movement 
up  or  down  ;  it  therefore  helps  the  spring  balance  to  support  the  weight 
and  makes  the  force  recorded  on  the  balance  a  little  less  than  the  real 
force.  The  real  force  is  the  average  of  the  forces  recorded  when  the 
weight  is  slowly  raised  and  slowly  lowered. 


LABORATORY  COURSE  IN  PHYSICS 
FORM   OF  REPORT 


II 


FORCE 

EXP. 

WEIGHT 

ROPES  SUPPORT- 
ING WEIGHT 

By  calculation 

By  experiment 

I 

lib. 

I 

2 

alb. 

2 

3 

3lb. 

3 

4 

2lb. 

4 

5 

6 

Method  2.  Repeat  the  experiments  given  above,  but  use  the 
following  weights:  (i)  500  g.  (2)  500  g.  (3)  600  g.  (4)  800  g. 
In  (2),  (3),  and  (4)  find  the  force  in  grams  required  to  support  the 
lower  pulleys  alone,  and  deduct  these  amounts  from  the  total 
forces  recorded  on  the  spring  balance.  Make  two  experiments 
of  your  own. 

FORM   OF  REPORT  . 


FORCE 

EXP. 

WEIGHT 

ROPES  SUPPORTING 
WEIGHT 

By  calculation 

By  experiment 

I 

500  g. 

I 

2 

500  g. 

2 

3 

600  g. 

3 

4 

800  g. 

4 

5 

6 

Does  the  law  of  the  pulley  hold  in  each  case ;  that  is,  is  the 
force  in  each  case  equal  to  the  weight  divided  by  the  number 
of  ropes  supporting  the  weight? 


12  LABORATORY  COURSE  IN  PHYSICS 

Exercise  2.     Pulley  and  Screw  Appliances. 

Name  any  pulley  appliances  in  the  school  and  state  the  advantage 
of  each. 

Measure  the  handle  and  pitch  of  at  least  two  of  the  following 
screw  appliances  and  calculate  their  advantage:  meat  chopper, 
faucet,  fruit  press,  sealer,  clamp.  Consult  page  17,  Physics  of 
the  Household. 

Make  a  rough  diagram  of  each  and  mark  on  it  the  length  of  the 
handle,  the  pitch,  and  the  advantage. 

Home  Exercise. 

Repeat  this  exercise  with  pulley  and  screw  appliances  in  your 
home. 

Make  a  written  report  on  this  work. 


LABORATORY  COURSE  IN  PHYSICS  13 

Experiment  4.     Common  weights  and  measures. 
To  study  some  common  weights  and  measures. 

Sheet  of  paper  15"  X  15".       Quart,  gallon. 

Yard  stick.  Balance  and  8  Ib.  weights. 

Cup,  pint.  Pail  of  f  cubic  foot  volume. 

Method  i.     The  linear,  square,  and  cubic  foot. 

On  a  piece  of  paper  draw  a  square  i  foot  on  each  side. 

Divide  it  into  square  inches  to  find  i  square  foot  contains 

square  inches. 

Hold  the  yard  stick  upright  at  one  corner  of  the  square.  Place 
your  thumb  i  foot  above  the  square  and  picture  to  yourself  the 
size  of  i  cubic  foot.  Find  by  calculation. 

i  cubic  foot  contains cubic  inches 

2.  Liquid  measure. 
With  water  find : 

the  number  of  cups  in  i  pint  = 
the  number  of  pints  in  i  quart  = 
the  number  of  quarts  in  i  gallon  = 

3.  Weight. 

Examine  the  pound  balance.     Turn  it  on  its  side  to  see  the  inside. 
Place  a  i  Ib.  weight  on  the  left  hand  pan  and  balance  it  by  means 
of  the  beam  weight.     Find : 

Each  division  on  the  beam  scale  = ounces. 

The  range  of  the  beam  scale         = ounces. 

To  show  that  i  cubic  foot  of  water  weighs  62.3  Ib.  Use  a  cubical 
til  ^  foot  long,  \  foot  wide,  and  \  foot  deep.  It  contains  \  X  J  X 
=  |  cubic  foot ;  therefore,  if  i  cubic  foot  of  water  weighs  62.3  Ib., 
lis  pail  should  hold  |  of  this  amount,  or  7  Ib.  12!  oz. 
Place  the  pail  on  one  pan  and  balance  it  with  weights.  Add 
Ib.  i2j  oz.  to  the  weight  pan  and  fill  the  pail  with  water. 

i  cubic  foot  of  water  weighs 

therefore  i  cubic  foot  of  water  weighs 


14  LABORATORY  COURSE  IN  PHYSICS 

Experiment  5.     Metric  weights  and  measures. 
To  study  metric  weights  and  measures. 

Sheet  of  paper  12"  X  12".         Quart  measure. 
Meter  stick.  Gram  balance. 

Liter  measure.  Pound  balance. 

Method  i.     The  linear,  square,  and  cubic  decimeter. 
Draw  a  line  and  mark  off  a  length  of  i  decimeter. 

(NOTE.  —  When  making  measurements  with  a  meter  stick,  yard  stick, 
etc.,  place  the  stick  on  its  edge  so  that  the  scale  may  be  brought  as  near 
as  possible  to  the  object  measured.) 

Divide  the  i  decimeter  into  centimeters  to  find : 
i  decimeter  = cm. 

Draw  a  square,  i  decimeter  on  each  side.  Divide  it  into  square 
centimeters  to  find : 

i  square  decimeter  = sq.  cm. 

Hold  the  meter  stick  upright  at  one  corner  of  this  square,  place 
your  thumb  i  dm.  above  the  square  and  picture  to  yourself  the 
volume  of  i  cubic  decimeter.  By  calculation  find : 

i  cubic  decimeter  = c.c. 

(i  cubic  decimeter  is  also  called  a  liter.) 

Measure  the  inside  diameter  and  depth  of  a  liter  measure  and 
calculate  its  volume  in  c.c.  to  find 

i  liter  = c.c. 

(NOTE.  —  The  volume  of  a  cylinder  =  TT  X  (radius)2  X  depth,  and  TT 
=  3.1416  or  -2/  nearly.) 

2.  Relation  between  volume  and  weight. 

Examine  the  gram  balance.  Remove  the  pans,  and  the  beam. 
Replace  them,  place  the  rider  at  zero,  and  balance  the  pans  by 
means  of  the  nut  at  the  right  hand  side  of  the  beam. 


LABORATORY  COURSE  IN  PHYSICS  15 

Place  a  10  g.  weight  on  the  left  pan  and  balance  it  by  means 
of  the  rider  to  determine : 

The  smallest  division  on  the  beam  scale  = g. 

The  range  of  the  beam  scale  = g. 

Place  a  liter  measure  on  the  left  pan  and  balance  it.  Then  add 
1000  g.  to  the  right  pan  and  fill  the  liter  measure  with  water  to 

find: 

i  liter  of  water  weighs g. 

.'.  i  c.c.  of  water  weighs g. 

3.  Relations  between  common  and  metric  measures. 
Draw  on  paper  a  line  10  inches  long  and  measure  it  in  centi- 
meters to  find : 

10  inches  = cm. 

.'.  i  inch      = cm. 

Use  a  liter  and  a  quart  measure  to  find : 

i  quart  = liters  (approx.) 

Weigh  a  i  Ib.  weight  in  grams  to  find : 

i  Ib.  = grams 

Weigh  a  kilogram  weight  in  pounds  to  find : 
i  kilogram  = Ib. 

Exercise  3.     Kitchen  Measuring  Appliances. 

A  well-equipped  kitchen  will  have  appliances  for  measuring 
volume,  weight,  oven  temperature,  and  time. 

Name  the  measuring  appliances  in  your  school  kitchen. 

Use  salt  to  find : 

the  number  of  level  teaspoonfuls  in  one  level  tablespoonful. 

the  number  of  level  tablespoonfuls  in  one  level  measuring  cup. 

Consult  page  305,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  this  exercise  with  the  measuring  appliances  in  your 
home  and  make  a  written  report  on  your  work. 


1 6  LABORATORY  COURSE  IN  PHYSICS 

Exercise  4.     Water  Supply. 

Describe  how  your  town  or  city  is  supplied  with  running  water. 
Does  the  water  come  from  a  distant  source  at  a  higher  level  than 
the  city ;  or  is  it  pumped  into  a  reservoir  ;  or  is  it  pumped  directly 
into  the  city  mains?  Is  the  water  purified,  and  if  so,  how? 

NOTE.  —  It  is  recommended  that  the  class  be  taken  to  the  city  pump- 
ing station,  the  filtering  plant,  and  the  reservoir. 

Make  a  diagram  of  the  city  water-supply  system  showing  the 
intake  pipe,  pumping  station,  filtering  plant,  and  one  water  main. 
Consult  page  30,  Physics  of  the  Household. 

Home  Exercise.     Tell  how  your  home  is  supplied  with  water. 

If  you  have  a  private  water  supply  system,  make  a  diagram  of  it 
showing  the  path  of  the  water  from  the  source  to  one  house  faucet. 

Make  a  written  report  on  this  work. 

Exercise  5.     Water  Supply  Plumbing. 

Examine  the  water  pipes  in  the  school.  Start  at  the  point  at 
which  the  water  enters  the  building  and  follow  the  pipes  to  the 
water  fixtures. 

Make  a  rough  diagram  showing  the  course  of  the  main  cold  water 
pipe  and  of  at  least  two  branches. 
•  Where  could  you  shut  the  water  off  in  case  a  water  pipe  burst? 

Home  Exercise.  Repeat  this  exercise  with  the  water  pipes  in 
your  own  home  and  make  a  written  report. 

Exercise  6.     Sewage  Plumbing. 

In  the  school  trace,  where  you  can,  the  path  of  the  waste  water 
from  each  fixture  to  the  point  at  which  it  leaves  the  building. 

Make  a  diagram  showing  the  main  soil  pipe  and  the  branches 
from  at  least  two  fixtures.  Consult  page  114,  Physics  of  the 
Household. 

What  becomes  of  the  sewage  after  it  leaves  the  building  ? ' 

Home  Exercise.  Repeat  this  exercise  in  your  own  home  and 
make  a  written  report. 


LABORATORY  COURSE  IN  PHYSICS  17 

Experiment  6.     Law  of  Archimedes. 

To  verify  the  law  of  Archimedes  for  bodies  that  sink  in  water 
and  for  bodies  that  float  on  water. 


m 


FIG.  10.     Apparatus  used  to  illustrate  the  law  of  ArchLnjeL., 


Twelve-quart  pail. 
Overflow  pail. 
Three-quart  pail. 
Spring  balance. 


Laboratory  support. 

Piece  of  rock  weighing  2  or  3  Ib. 

Block  of  wood. 


The  law  of  Archimedes  is :   A  body  when  placed  in  a  liquid  loses 
weight  equal  to  the  weight  of  liquid  displaced. 


1 8  LABORATORY   COURSE   IN   PHYSICS 

Method.    Bodies  that  sink  in  water. 

To  find  the  loss  in  weight.  Weigh  the  piece  of  rock  (Fig.  10) 
on  a  spring  balance  suspended  from  a  stand.  This  is  the  weight 
of  the  rock  in  air.  Now  suspend  the  rock  in  a  i2-quart  pail  of 
water  and  find  its  weight  in  water.  The  difference  is  the  loss  in 
weight  in  water. 

weight  of  rock  in  air        = 

weight  of  rock  in  water  = 

loss  in  weight  = 

To  find  the  weight  of  water  displaced  by  the  rock.  Fill  the  over- 
flow pail  with  water  until  water  runs  out  at  the  spout.  Weigh 
the  empty  catch  pail.  Then  lower  the  piece  of  rock  slowly  into 
the  overflow  pail  and  catch  the  water  which  overflows.  Weigh 
the  catch  pail  with  the  displaced  water. 

weight  of  catch  pail  +  water  = 

weight  of  catch  pail  empty      = 

weight  of  water  displaced        = 

You  have  now  found  the  loss  in  weight  when  the  rock  is  weighed 
in  air  and  then  in  water,  also  the  weight  of  water  displaced  by  the 
rock.  Is  the  loss  in  weight  equal  to  the  weight  of  water  displaced  ? 
That  is,  do  you  verify  the  law  of  Archimedes  for  this  heavy  body  ? 
Bodies  that  float  on  water.  Repeat  the  experiment  above,  but 
use  a  block  of  wood  instead  of  the  piece  of  rock. 

weight  of  wood  in  air  = 

weight  of  wood  on  water          = 

loss  in  weight  = 


weight  of  catch  pail  +  water  = 
weight  of  catch  pail  empty  = 
weight  of 


Do  you  notice  that  the  block  of  wood  loses  all  of  its  weight  when 
placed  in  water  ?  Is  this  loss  in  weight  equal  to  the  weight  of  the 
liquid  it  displaces,  that  is,  do  you  verify  the  law  of  Archimedes  for 
this  floating  body  ? 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  7.     Volume  and  density. 

To  learn  how  to  find  the  volume  and  density  of  a  body. 


FIG.   it.     Apparatus  used  to  find:    the  volume  of  a  body  in  three  ways,  and  the 
density  of  a  substance. 


A  solid  metal  cylinder. 
Vernier  calipers. 
Micrometer  calipers. 
Graduated  cylinder  100  c.c. 


Density  balance. 
Vessel  containing  water. 
Overflow  pail. 
Catch  pail. 


VOLUME 

We  will  find  the  vo)^  Ha  solid  ind^j^^s :  (i)  by  measure- 
ment, (2)  by  finding  tn^BBime  oOquM  it  displaces  when  entirely 
immersed,  (3)  by  finds  Jtfttfn  wa^er- 

Method  i .     To  find  the  ^^mKJpmder  by  measurement^ 

Measure  the  length  of  the  cylinder  three  times  by  means  of  the 
vernier  calipers  and  find  the  average  length. 

Measure  the  diameter  of  the  cylinder  in  three  places  by  means 
of  the  micrometer  calipers  and  find  the  average  diameter. 


20  LABORATORY  COURSE  IN  PHYSICS 

NOTE.  —  If  the  laboratory  is  not  supplied  with  these  calipers,  make 
the  measurements  with  a  meter  stick. 

Calculate  the  volume  of  the  cylinder  in  c.c.  Volume  of  cylinder 
=  TT  X  (radius)2  X  length. 

Method  2.  To  find  the  volume  of  a  body  by  finding  the  volume 
of  liquid  it  displaces. 

It  is  evident  that  if  the  volume  of  a  solid  is,  say  100  c.c.,  it  will 
displace  100  c.c.  of  a  liquid  if  immersed  in  the  liquid.  If  its  volume 
is  150  c.c.  it  will  displace  150  c.c.  of  the  liquid,  etc.  In  other  words 
the  solid  will  displace  its  own  volume  of  the  liquid. 

Fill  an  overflow  pail  with  water  and  when  it  has  stopped  dripping 
immerse  the  cylinder  in  the  water.  Catch  the  water  which  over- 
flows and  measure  its  volume  in  c.c.,  using  measuring  flask  or 
graduated  cylinder  The  volume  of  the  liquid  displaced  is  equal 
to  the  volume  of  the  cylinder  immersed. 

Method  3.  To  find  the  volume  of  a  body  by  finding  its  loss  in 
weight  in  water.  In  your  experiment  on  the  law  of  Archimedes 
you  learned  that  the  loss  in  weight  of  a  body  when  immersed  in 
water  is  equal  to  the  weight  of  the  water  it  displaces.  That  is,  if 
a  body  loses  100  g.  in  weight  when  weighed  in  water,  it  will  dis- 
place 100  g.  of  water  and,  since  i  g.  of  water  has  a  volume  of  i  c.c., 
it  will  displace  100  c.c.  of  water,  that  is,  its  volume  is  100  c.c.  In 
other  words,  the  loss  in  weight  in  grams  of  a  body  immersed  in  water 
is  equal  to  its  volume  in  c.c. 

Find  the  weight  in  g.  of  the  cylinder  in  air,  then  find  its  weight 
when  immersed  in  water.  The  difference  is  its  loss  in  weight  in 
grams  and  therefore  its  volume  in  c.c. 

DENSITY 

The  density  of  a  substance  is  defined  as  the  weight  of  unit  volume 
of  that  substance;  that  is,  it  is  the  weight  of  i  cu.  ft.,  i  cu.  in., 
i  c.c.,  etc.  In  all  scientific  work,  unless  otherwise  stated,  the 
density  of  a  substance  is  the  weight  in  g.  of  i  c.c.  of  the  substance. 

To  find  the  density  of  aluminium. 


LABORATORY  COURSE  IN  PHYSICS  21 

The  cylinder  you  used  above  is  made  of  aluminium  and  you 
have  found  its  volume  in  c.c.  and  its  weight  in  air  in  g.  Use  the 
volume  found  in  method  i,  and  the  weight  in  air  found  in  method 
3,  to  find  the  density  of  aluminium  as  follows : 

....  c.c.  of  aluminium  weigh g. 

.'.  i  c.c.  of  aluminium  weighs .g. 

the  density  of  aluminium. g.  per  c.c. 

FORM    OF   REPORT 

VOLUME 

i          2         3     average 

Method  i.   Length  of  cylinder  in  cm.  = 

Diameter  of  cylinder  in  cm.          = 

Volume  of  cylinder  = c.c. 

Method  2.  Volume  of  water  displaced  in  c.c.  = 

Volume  of  cylinder  = c.c. 

Method  j.  Weight  of  cylinder  in  g.  in  air  = 

Weight  of  cylinder  in  g.  in  water  = 

Loss  in  weight  in  g.  = 

Volume  in  c.c.  .  = 

*  DENSITY 

Weight  of  cylinder  of  aluminium  in  air     = g. 

Volume  of  cylinder  = c.c. 

Density  =    weighting.     =  ..g.perc.c. 

volume  in  c.c. 


22 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  8.     Density  of  solids. 

To  find  the  density  of  a  number  of  solids. 


FIG.   12.     Apparatus  used  to  find  the  density  of  rock  and  iron. 

Density  balance.  Pieces  of  rock,  and  of  iron  weighing 

Large  vessel  of  water.  500  or  600  g. 

As  was  stated  in  Experiment  7,  the  density  of  a  substance  is  the 
weight  in  grams  of  one  cubic  centimeter  of  the  substance.     In 
Experiment  7  we  found  that  the  volume  of  a  solid  in  c.c.  is  equal 
to  its  loss  in  weight  in  g.  when  weighed  in  air  and  then  in  water. 
Method.     Find  the  density  of  rock  and  of  iron  as  follows : 
Attach  a  cord  to  the  solid  and  weigh  it  in  air  on  the  density 
balance,  Fig.  12.     Then  immerse  it  in  water  and  find  its  weight 
in  water.     The  difference  is  its  loss  in  weight  in  g.  and  its  volume 
in  c.c. 

Calculate  the  density. 

Density  =  weight  in  air  ing. 
volume  in  c.c. 


LABORATORY   COURSE   IN   PHYSICS 


FORM    OF   REPORT 


ROCK 

IRON 

Weight  in  air  in  g. 
Weight  in  water  in  g. 
Loss  in  weight  in  g. 
Volume  in  c.c. 
Density  in  g.  per  c.c. 

LABORATORY  COURSE  IN  PHYSICS 


Experiment  9.     Density  of  liquids. 
To  find  the  density  of  a  liquid. 


FIG.  13.     Apparatus  used  to  find  the  density  of  liquids. 


Density  bottle. 
Gram  scales. 
Hydrometer. 


Hydrometer  jar. 
Kerosene,  gasoline, 
vinegar,  or  alcohol. 


Method  i.  Find  the  weight  in  g.  of  the  density  bottle,  Fig.  13, 
when  empty.  Then  find  its  weight  when  filled  with  water.  The 
difference  is  the  volume  of  the  bottle  in  c.c.,  because  i  g.  of  water 
has  a  volume  of  i  c.c.  (If  the  volume  of  the  bottle  is  known,  it  is 
not  necessary  to  find  its  weight  when  filled  with  water.)  Fill  the 
bottle  with  the  liquid,  dry  the  outside,  and  find  the  weight  of 


LABORATORY  COURSE  IN  PHYSICS  25 

bottle  +  liquid.  Subtract  from  this  the  weight  of  the  empty  bottle 
to  find  the  weight  of  the  liquid.  Calculate  the  density  of  the  liquid 
as  follows  : 


Density  _  ,  --  ......  g.  per  c.c. 

volume  of  liquid  in  c.c. 

Method  2.     Find  the  density  by  means  of  a  hydrometer  as  follows  : 
Fill  a  cylinder,  Fig.  13,  with  the  liquid  and  place  the  hydrometer 

in  it.     Read  the  scale  division  opposite  the  surface  of  the  liquid. 

This  is  the  density  of  the  liquid  in  g.  per  c.c. 

FORM   OF   REPORT 

Weight  of  bottle  -f  water  =  .  .  .  .  g.  Weight  of  bottle  +  liquid  =  .  .  .  .  g. 
Weight  of  empty  bottle  =  .  .  .  .  g.  Weight  of  empty  bottle  =  .  .  .  .  g. 
Weight  of  water  =  .  .  .  .  g.  Weight  of  liquid  =  .  .  .  .  g. 

Volume  of  bottle  =  .  .  .c.c.  Density  of  liquid  =  .  .  .  .g.  per  c.c. 

Density  of  liquid  by  means  of  hydrometer  ............  g.  per  c.c. 

(See  table  of  densities  page  138.) 

Exercise  7.     Gas  Plumbing. 

Trace  the  gas  pipes  from  the  point  at  which  the  gas  enters  the 
school  to  each  gas  fixture. 

Make  a  diagram  showing  the  course  of  the  main  gas  pipe  and 
of  at  least  two  branches. 

Is  your  city  supplied  with  natural  gas  or  manufactured  gas? 
If  natural  gas,  tell  where  it  comes  from.  If  manufactured  gas, 
tell  how  it  is  made. 

Home  Exercise. 

Repeat  this  exercise  in  your  own  home  and  make  a  written 
report. 

Read  your  gas  meter  once  each  month  for  six  months  ;  record 
the  readings  and  dates,  and  compare  your  readings  with  those 
made  by  the  gas  company. 


26  LABORATORY  COURSE  IN  PHYSICS 

Experiment  10.     Barometer  and  siphon. 

To  construct  a  barometer  and  to  measure  the  pressure  of  the 
atmosphere  with  it.  To  illustrate  the  action  of  the  siphon. 

Two  barometer  tubes  of  different  Siphon. 

length  and  diameter.  Two  pails  of  water 

Two  evaporating  dishes.  Meter  stick. 

Mercury.  Support. 
Small  funnel. 

BAROMETER 

Method.  Fill  a  barometer  tube  with  mercury,  place  the  finger 
over  the  open  end,  invert  the  tube  over  a  shallow  dish  of  mercury 
and  remove  the  finger  under  mercury.  Measure,  in  cm.  and  also 
in  inches,  the  height  of  the  column  of  mercury  in  the  tube  above 
that  in  the  dish. 

Repeat  the  experiment  with  the  second  barometer  tube. 

You  will  notice  that  the  columns  of  mercury  are  practically  of 
the  same  height  although  you  have  used  tubes  of  different  areas 
of  cross  section,  Fig.  14.  (They  would  be  of  exactly  the  same 
height  if  all  the  air  were  removed  from  the  space  above  the  mer- 
cury.) We  should  find  the  heights  to  be  the  same  if  we  made 
experiments  with  many  tubes  of  different  cross  section.  That  is, 
the  height  of  the  column  of  mercury  is  independent  of  the  area  of 
cross  section  of  the  tube.  This  being  the  case  we  can  consider 
the  area  of  cross  section  of  the  tube  to  be  anything  we  wish,  for 
example,  i  sq.  in.  or  i  sq.  cm. 

To  find  the  pressure  of  the  atmosphere  in  Ib.  per  sq.  in.  Assume 
that  the  tube  has  an  area  of  cross  section  of  i  sq.  in.  Multiply 
this  by  the  height  of  the  column  of  mercury  in  inches  to  obtain 
the  number  of  cubic  inches  of  mercury  in  the  column.  Multiply 
the  result  by  .49  Ib.,  the  weight  of  i  cubic  inch  of  mercury. 

To  find  the  pressure  of  the  atmosphere  in  g.  per  sq.  cm.  Assume 
that  the  tube  has  an  area  of  cross  section  of  i  sq.  cm.  Multiply 


LABORATORY   COURSE  IN  PHYSICS  27 


FIG.  14.    Apparatus  used  to  illustrate  the  action  of  the  barometer  and  the  siphon. 


28 


LABORATORY   COURSE   IN  PHYSICS 


this  by  the  height  of  the  column  of  mercury  in  cm.  and  multiply 
the  result  by  13.6  g.,  the  weight  of  i  c.c.  of  mercury. 

SIPHON 

Method.  Make  a  U  tube  by  connecting  two  glass  tubes  3  or  4 
feet  long  by  means  of  a  rubber  tube,  1.5  feet  long.  Fill  this  U 
tube  with  water,  place  a  finger  over  each  end,  invert  the  tube, 
place  the  ends  in  separate  pails  half  full  of  water  and  remove  the 
fingers  under  water. 

Lower  one  pail  and  notice  the  direction  in  which  the  water 
flows.  Raise  this  pail  and  lower  the  other.  Is  the  direction  of 
the  flow  reversed? 

FORM    OF   REPORT 


Pressure 

i 

2 

AVERAGE 

Height  of  mercury 
Height  of  mercury 

in. 
cm. 

in. 
cm. 

Df  atmosphere  Ib.  per  sq.  in. 

Pressure  of  atmosphere  g.  per  sq.  cm. 

Exercise  8.     Plumbing  Traps. 

Locate  the  trap  under  each  type  of  water  fixture  in  the  school. 

Open  a  trap  under  a  sink  or  washbowl  and  clean  it  out. 

Make  a  diagram  showing  the  path  of  the  water  through  the 
trap,  and  showing  how  the  water  seal  is  formed.  Consult  page  73, 
Physics  of  the  Household. 

Home  Exercise. 

Repeat  this  exercise  in  your  own  home  and  make  a  written 
report. 


LABORATORY   COURSE  IN  PHYSICS 


Experiment  11.     Boyle's  Law. 

To  illustrate  Boyle's  Law. 


FIG.  15.     Apparatus  used  to  illustrate  Boyle's  Law. 

Capillary  tube  no  cm.  long  with  a  column  of  air  between 

a  column  of  mercury  and  the  closed  end.1 
Support.  Meter  stick. 

Boyle's  Law  is :  The  volume  of  a  gas  varies  inversely  as  the  pres- 
sure on  it.  That  is,  if  the  pressure  on  the  gas  is  doubled,  it  is 

1  If  this  tube  is  not  filled,  fill  it  as  follows.  Draw  a  column  of  mercury  about  50 
cm.  long  into  the  tube;  close  one  end  with  the  finger  and  allow  a  column  of  air  about 
20  cm.  long  to  enter  the  other  end.  Seal  the  latter  end  with  sealing  wax. 


30  LABORATORY  COURSE   IN   PHYSICS 

compressed  to  half  its  first  volume ;  if  the  pressure  is  halved,  the 
gas  expands  to  twice  its  first  volume,  etc. 

Method.  You  have  on  the  table  a  tube  which  has  a  certain 
amount  of  air  between  a  column  of  mercury  and  the  closed 
end. 

Lay  the  tube  on  the  table  and  notice  the  length  of  the  air 
column.  Now  stand  it  upright,  with  the  closed  end  down,  and 
notice  that  the  air  is  compressed  because  the  pressure  on  it  is 
increased.  Stand  the  tube  upright,  with  the  closed  end  up; 
notice  that  the  air  expands  because  the  pressure  on  it  is  de- 
creased. 

(1)  Lay  the  tube  on  the  table  and  measure  the  length  Vi  in 
cm.  of  the  air  column  and  also  the  length  in  cm.  of  the  mercury 
column. 

In  this  position  the  mercury  is  not  exerting  pressure  on  the 
gas  and  the  total  pressure  PI  on  the  gas  is  i  atmosphere.  If  there 
is  a  barometer  in  the  laboratory  measure  its  height.  If  not,  take 
the  height  of  the  barometer  to  be  76  cm.  (i  atmosphere).  Since 
the  bore  of  the  tube  is  uniform  we  may  use  the  length  of  the  air 
column  as  a  measure  of  the  volume  of  the  air  under  different 
pressures. 

(2)  Stand   the   tube   upright  with   the  closed   end   down   and 
measure  the  length  ¥2  of  the  air  column.     The  pressure  P2  on  the 
air  in  the  tube  is  76  cm.  (i  atmosphere)  +  the  length  of  the  mer- 
cury column  in  cm. 

(3)  Stand  the  tube  upright  with  the  closed  end  up  and  measure 
the  length  Vs  of  the  air  column.     The  pressure  Pa  on  the  air  in 
the  tube  is  76  cm.  (i  atmosphere)  —  the  length  of  the  mercury 
column. 

If  the  volume  of  the  gas  varies  inversely  as  the  pressure  on  it 

P  Vi         P3  Vi 

(Boyle's  Law) ,  then  —  should  equal  —  and  =-  should  equal  —  • 
"i  V2  Jri  Vs 

That  is,  the  volume  of  the  air  should  be  decreased  in  the  pro- 
portion the  pressure  is  increased,  and  vice  versa. 


LABORATORY   COURSE  IN  PHYSICS 


FORM    OF   REPORT 


PRESSURE 

VOLUME 

I 

76  cm. 

cm. 

2 

76  +     cm. 

cm. 

3 

76  —      cm. 

cm. 

PI 

£§ 
PI 


V2 

X-i 

V3 


Do  you  verify  Boyle's  Law,  that  is,  when  the  pressure  on  the 
gas  is  increased  in  (2)  is  the  volume  decreased  in  proportion ;  and 
when  the  pressure  on  the  gas  is  decreased  in  (3)  is  the  volume 
increased  in  proportion? 

Exercise  9.     Fire  Extinguisher. 

Examine  the  interior  of  one  of  the  fire  extinguishers  in  the 
school. 

Close  it,  take  it  out-of-doors,  turn  it  upside  down  and  discharge 
it  at  a  small  bonfire,  if  convenient. 

Charge  the  extinguisher  according  to  the  directions  on  the  case, 
then  discharge  it  again  to  make  sure  that  you  have  done  the  work 
properly. 

Charge  it  again  and  hang  it  where  it  will  be  convenient  for 
immediate  use. 

Make  a  diagram  showing  the  interior  of  the  extinguisher. 
Consult  page  70,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  this  exercise  with  the  fire  extinguisher  in  your  home 
and  make  a  written  report. 

Exercise  10.     Vacuum  Cleaner. 

If  there  is  a  vacuum  cleaner  in  the  school,  examine  it  to  learn : 

1.  how  a  partial  vacuum  is  produced ; 

2.  the  path  along  which  the  air  travels ; 

3.  how  the  air  is  freed  from  dirt. 


32  LABORATORY   COURSE  IN  PHYSICS 

Make  a  rough  diagram  showing  the  path  of  the  air  through  the 
cleaner. 

Home  Exercise. 

Repeat  this  exercise  with  the  vacuum  cleaner  in  your  own  home 
and  make  a  written  report. 


LABORATORY   COURSE   IN   PHYSICS 


33 


HEAT 

Experiment  12.     Thermometers. 

To  find  the  fixed  points  of  a  Fahrenheit  thermometer  and  of  a 
centigrade  thermometer. 


Two  types  of  apparatus  used  to  find  the  fixed  points  of  thermometers. 


FIG.  16. 


Glass  full  of  snow  or  ice,  and  water. 
Fahrenheit  thermometer. 
Centigrade  thermometer. 


Boiler. 

Tripod. 

Burner. 


The  fixed  points  of  a  thermometer  are  the  temperature  of  melting 
ice  or  snow  and  the  temperature  of  the  steam  formed  by  water  boiling 
under  a  pressure  of  one  atmosphere. 

Method.  To  find  the  temperature  of  melting  ice  or  snow.  Fill 
a  glass  with  snow  or  ice  and  add  a  little  water.  Place  the  ther- 
D 


34  LABORATORY   COURSE  IN  PHYSICS 

mometers  in  this  and  note  the  lowest  temperature  recorded  on 
each.  If  the  thermometers  do  not  record  o°  on  the  centigrade 
and  32°  on  the  Fahrenheit,  it  is  the  thermometers  which  are  in 
error  and  not  the  ice.  Record  the  error  of  each. 

To  find  the  temperature  of  the  steam  formed  by  water  boiling 
under  a  pressure  of  one  atmosphere.  Pour  water  into  the  boiler, 
on  the  right,  Fig.  16,  to  a  depth  of  2  or  3  inches.  Pass  the  top  of 
the  thermometer  through  one  hole  of  a  two-holed  stopper  until 
the  100°  C.  or  212°  F.  line  is  just  exposed  but  with  the  bulb  above 
the  water  in  the  boiler.  Place  a  bent  tube  in  the  other  hole  to 
divert  the  steam  and  insert  the  stopper  in  the  opening  of  the 
boiler.  If  you  use  a  boiler  similar  to  that  on  the  left,  Fig.  16,  pass 
the  thermometer  through  a  one-hole  stopper  and  allow  the  steam 
to  escape  from  the  outlet  beneath.  Boil  the  water  and  allow  the 
steam  to  pass  for  one  or  two  minutes.  Read  the  temperature 
and  if  the  barometer  stands  at  76  cm.  (i  atmosphere  exactly) 
note  the  error  of  the  thermometer. 

Repeat  with  the  other  thermometer. 

FORM    OF   REPORT 

FAHRENHEIT  CENTIGRADE 

Temperature  of  melting  ice °  F.  °  C. 

Error  of  thermometer °  F.  °  C. 

Temperature  of  steam °  F.  °  C. 

Error  of  thermometer °  F.  °  C. 

Exercise  11.     Thermometers. 

Examine  the  wall  thermometer  in  the  school  and  observe  how 
high  and  how  low  it  reads. 

Make  a  diagram  of  the  scale. 

Examine  the  oven  thermometer  on  the  school  range. 

Make  a  diagram  representing  its  working  parts. 

Home  Exercise. 

Repeat  these  exercises  with  the  thermometers  in  your  home  and 
make  a  written  report. 


LABORATORY   COURSE   IN  PHYSICS  35 

Experiment  13.     Expansion  of  brass. 

To  find  the  coefficient  of  linear  expansion  of  brass. 

Steam  1' 


\* 

L 


A 

FIG.  17.     Diagram  of  the  apparatus  used  to  measure  the  linear  coefficient  of  expan- 
sion of  brass. 


Expansion  apparatus.  Burner. 

Boiler.  Thermometer. 


The  coefficient  of  linear  expansion  is  the  expansion  per  unit  length 
per  degree  change  in  temperature.  We  will  determine  the  expansion 
in  cm.  of  a  tube  of  brass  i  cm.  long  for  a  change  in  temperature 
of  i°C. 

Method.  Measure  in  cm.  the  length  of  the  pointer  CD,  Fig.  17, 
from  the  end  D  to  the  middle  of  the  arm  AB.  Measure  the  arm 
AB  by  means  of  the  micrometer  calipers  (or  meter  stick  if  the 
calipers  are  not  available).  Divide  the  length  of  the  pointer 
CD  by  the  length  of  the  arm  AB  to  determine  how  many  times  a 
movement  of  B  is  magnified  by  D. 

Clamp  or  secure  the  brass  tube  at  the  point  P  near  one  end 
and  place  the  pointer  in  position  near  the  other  end.  Find  the 
length  in  cm.  of  the  tube  between  P  and  B.  Place  the  thermometer 
in  the  tube  at  end  P  and  record  the  temperature  of  the  tube. 

When  everything  is  ready  read  carefully  and  record  the  position 
of  the  end  D  of  the  pointer  on  the  scale.  Then  place  the  burner 
under  the  boiler  and  allow  the  steam  to  pass  freely  for  one  or  two 
minutes.  Read  carefully  and  record  the  new  position  of  the 
pointer  D,  and  the  temperature  of  the  steam.  Calculate  the 
coefficient  of  expansion  of  brass,  that  is,  the  expansion  in  cm.  of  a 
tube  i  cm.  long  for  a  change  in  temperature  of  i°  C. 

Example.  A  brass  tube  is  90  cm.  long  from  P  to  B.  The  pointer 
CD  is  22.5  cm.  long  and  the  arm  AB  is  1.5  cm.  long.  The  end  of  the 


36  LABORATORY   COURSE  IN  PHYSICS 

pointer  moves  2  cm.  when  the  temperature  changes  from  20°  to  100°  C 
What  is  the  coefficient  of  expansion  of  the  brass  ? 

Pointer  magnifies  22.5  -f-  1.5  =  15  times. 

Actual  expansion  =  2  -r-  15  =  .133  cm. 

A  bar  90  cm.  long  warmed  80°  C.  expands  .133  cm. 

A  bar  i  cm.  long  warmed  i°  C.  expands  '-^ '-  • 

go  X  80 

Coefficient  of  expansion  =  — ^^ —  =  .000018. 
90  X  80 


FORM    OF   REPORT 


Length  of  pointer  =  cm.   Length  of  brass  tube          =      cm. 

Length  of  arm  =  cm.   Temperature  at  beginning  =      °  C. 

Magnification  of  pointer     =  Temperature  at  end  =      °  C. 

Pointer  reading  beginning  =  cm.  Difference  =      °  C. 

Pointer  reading  end  =  cm. 

Difference  cm. 
Coefficient  of  expansion  of  brass  = 


LABORATORY   COURSE   IN   PHYSICS 


37 


Experiment  14.     Expansion  of  air. 

To  find  the  volume  coefficient  of  expansion  of  air. 


_- 


FIG.  1 8.     Apparatus  used  to  measure  the  coefficient  of  volume  expansion  of  air. 

Flask  about  1000  c.c.  Pail,  i2-qt. 

Rubber  stopper  with  one  hole.  Stand. 

Tube  and  clip.  Burner. 

Measuring  cylinder,  1000  c.c.  Ice 

Pail,  3-qt. 

The  volume  coefficient  of  expansion  of  any  gas  is  the  expansion, 
per  degree  change  in  temperature,  of  unit  volume  measured  at 
o°C. 

Method.  We  will  heat  a  volume  of  air  to  100°  C.  and  then  cool 
it  to  o°  C.  and  find  how  much  it  contracts  in  volume.  This  con- 


38'  LABORATORY  COURSE  IN  PHYSICS 

traction  is  the  same  as  the  expansion  would  be  if  we  did  the  re- 
verse, that  is,  started  at  o°  C.  and  heated  the  air  to  100°  C. 

Place  the  dry  flask  with  stopper  and  clip  in  a  3-qt.  pail  of  water 
as  shown  in  Fig.  18.  Boil  the  water  vigorously  for  2  or  3  minutes, 
then  close  the  clip  and  invert  the  flask  in  a  i2-qt.  pail  of  ice  water. 
Open  the  clip  under  water  and  allow  the  water  to  enter.  Close 
the  clip,  remove  the  flask  and  measure  the  volume  of  water  which 
entered.  Now  fill  the  flask  with  water  to  the  bottom  of  the  stopper 
and  find  its  total  volume. 

Calculate  the  volume  coefficient  of  expansion  of  the  air  as  fol- 
lows :  The  volume  of  the  air  at  100°  C.  is  equal  to  the  total  volume 
of  the  flask.  The  volume  of  the  air  at  o°  C.  is  equal  to  the  total 
volume  of  the  flask  minus  the  volume  of  water  which  entered  the 
flask.  The  volume  of  the  water  which  entered  is  the  volume  this 
air  at  o°  C.  would  expand  when  warmed  for  o°  C.  to  100°  C. 

Example.  The  total  volume  of  the  flask  =  1189  c.c. 
The  volume  of  the  water  which  entered  =  319  c.c. 
The  volume  of  the  air  at  o°  C.  =  870  c.c. 

870  c.c.  of  air  at  o°  C.  warmed  100°  C.  expand  319  c.c. 

i  c.c.  of  air  at  o°  C.  warmed  i°  C.  expands  — ^ =  .00366. 

870  X  ioo 

Volume  coefficient  of  expansion  of  air  =  .00366. 

FORM  OF  REPORT 

Total  volume  of  the  flask,  or  the  volume  of  the  air  at  100°  C.  = . . .  .c.c. 
The  volume  of  water  which  entered  flask  =.  . .  .c.c. 

The  volume  of  the  air  at  o°  C.  = . . . .  c.c. 

Change  of  temperature  =  100°  C. 
Volume  coefficient  of  expansion  of  air  = 

Exercise  12.     Kitchen  Range. 

Examine  the  range  in  the  school  kitchen  and  trace  the  path 
of  the  air  from  the  point  at  which  it  enters  the  range  to  the  point 
at  which  it  enters  the  stovepipe.  Consult  page  93,  Physics  of 
the  Household. 


LABORATORY   COURSE  IN  PHYSICS  39 

Make  a  diagram  showing  the  path  of  the  air  through  the  range 
hen  the  oven  is  "  on."     Mark  on  it  the  position  of  each  damper. 
Describe  the  use  of  each  damper. 
Tell  why  the  range  "  draws." 
Home  Exercise. 

Repeat  this  exercise  with  the  range  in  your  home  kitchen  and 
make  a  written  report. 

Exercise  13.     Heating  System. 

Examine  the  heating  system  of  the  school.  Follow  the  pipes 
from  the  furnace  to  each  radiator  or  register. 

Is  the  school  heated  by  means  of  hot  air,  hot  water,  or  steam? 

Make  a  diagram  showing  the  path  of  the  air,  water,  or  steam, 
from  the  furnace  to  at  least  two  radiators  or  registers.  Consult 
pages  95,  96,  139,  Physics  of  the  Household. 

Explain  why  the  air,  water,  or  steam  moves  as  it  does. 

Home  Exercise. 

Repeat  this  exercise  with  the  heating  system  in  your  own  home 
and  make  a  written  report. 

Exercise  14.     Hot- Water  Boiler. 

Examine  the  system  which  supplies  running  hot  water  to  the 
school  kitchen. 

Make  a  diagram  illustrating  this  system. 

Home  Exercise. 

Describe  how  your  home  kitchen  is  supplied  with  running  hot 
water. 

Make  a  diagram  showing  where  the  cold  water  enters,  how  it 
is  heated,  and  where  the  hot  water  leaves.  Consult  page  97, 
Physics  of  the  Household. 

Make  a  written  report. 


LABORATORY   COURSE  IN  PHYSICS 


Experiment  15.     How  to  measure  heat. 

PART  I:  To  illustrate  the  meaning  of  the  heat  units:   British 
Thermal  Unit,  calorie,  and  kilogram  calorie. 


FIG.  19.     Apparatus  used  to  illustrate  the  heat  units,  and  to  show  that  different 
substances  at  the  same  temperature  may  contain  different  quantities  of  heat. 


Pail,  3-qt- 
Balance,  Ib. 


Thermometers. 
Burner  and  tripod. 
Measuring  cylinder,  1000  c.c. 


The  British  Thermal  Unit  (B.T.U.)  is  the  amount  of  heat  required 
to  raise  the  temperature  of  i  Ib.  of  water  i°  F. 

The  calorie  is  the  amount  of  heat  required  to  raise  the  temperature 
of  i  g.  of  water  i°  C. 

The  kilogram  calorie  1  or  Calorie  is  the  amount  of  heat  required  to 

1  When  the  term  calorie  is  met  in  discussions  of  food  values  and  the  energy  require- 
ments of  nutrition,  it  will  almost  invariably  be  found  to  refer  to  the  kilogram  calorie. 
The  use  of  the  capital  C  indicates  that  the  greater  calorie  is  intended.  Many  writers 
on  food  and  nutrition  use  the  simple  term  calorie  for  the  kilogram  calorie,  assuming  that, 
readers  will  not  be  in  doubt  as  to  which  calorie  is  meant  inasmuch  as  the  two  units 
differ  by  a  thousandfold. 


LABORATORY   COURSE   IN  PHYSICS  41 

raise  the  temperature  of  i  kg.  of  water  i°  C.  The  kilogram  calorie 
=  1000  calories. 

Method.  British  Thermal  Unit.  Weigh  an  empty  three-quart 
pail  and  add  to  it  a  certain  weight  of  cold  water,  say  4  Ib.  Find 
the  temperature  of  the  water  in  Fahrenheit  degrees. 

Place  the  pail  over  a  burner  for  2  minutes  and  again  find  its  tem- 
perature. Calculate  the  number  of  B.T.U.  received  by  the  water. 

Place  the  pail  in  a  cool  place  for  2  minutes  and  find  its  tempera- 
ture. Calculate  the  number  of  B.T.U.  lost  by  the  water. 

Method.  Calorie  and  kilogram  calorie.  Measure  out  2000  c.c. 
(2000  g.)  of  cold  water  and  pour  it  into  the  pail.  Find  the  tem- 
perature of  the  water  in  centigrade  degrees. 

Place  the  vessel  over  a  burner  for  2  minutes  and  again  find  its 
temperature.  Calculate  the  number  of  calories  received  by  the 
water.  Calculate  the  number  of  kilogram  calories  or  Calories  re- 
ceived by  the  water. 

Place  the  vessel  in  a  cool  place  for  2  minutes  and  find  its  tempera- 
ture. Calculate  the  number  of  calories  lost  by  the  water.  Calcu- 
late the  number  of  kilogram  calories  or  Calories  lost  by  the  water. 

FORM    OF   REPORT 

The  ....  Ib.  of  water  was  warmed  from  ....  °  F.  to  ....  °  F. .'.  gain  =  . . . . 

B.  T.  U. 
. . .  .  Ib.  of  water  was  cooled  from  .  . .  .°  F.  to  ...  .°  F.  .'.  loss  =  . . .  * 

B.  T.  U. 
The  ....  g.  of  water  was  warmed  from  ....  °  C.  to  ....  °  C. .'.  gain  =  . . . . 

calories. 
The  ....  g.  of  water  was  cooled  from  .... °  C.  to  .... °  C. .'.  loss  =  . . . . 

calories. 
The  ....  kg.  of  water  was  warmed  from  .  . .  .  °  C  to  .  . .  .  °  C. .'.  gain  = 

Calories. 
The  ....  kg.  of  water  was  cooled  from  ....  °  C.  to  ....  °  C. .'.  loss  = 

Calories. 

PART  II.  To  show  that  different  substances  at  the  same  tempera- 
ture may  contain  different  quantities  of  heat. 


42  LABORATORY   COURSE   IN   PHYSICS 

Three  3-qt.  pails.  Burner. 

Balance,  Ib.  Tripod. 

Iron  weight,  3  or  4  Ib.  Fahrenheit  thermometer. 

Hot  water  (in  a  hot  water  bag)  and  hot  iron  (a  hot  flat-iron) 
are  frequently  used  as  footwarmers.  Let  us  compare  the  amounts 
of  heat  given  up  on  cooling  by  equal  weights  of  hot  water  and  hot 
iron  at  the  same  temperature.  Proceed  as  follows : 

Method.  Place  a  pail  on  one  pan  of  a  scales  and  balance  it ; 
then  place  an  iron  weight  on  the  other  pan  and  add  enough  water 
to  the  pail  to  balance  the  iron.  We  now  have  equal  weights  of 
water  and  iron. 

Place  the  iron  in  the  pail,  cover  the  pail  and  heat  until  the  water 
boils  vigorously.  We  now  have  equal  weights  of  iron  and  water 
at  212°  F. 

While  the  water  and  iron  are  being  heated,  weigh  two  empty 
pails  and  add  to  each  equal  weights  of  cold  water,  say  2  Ib.  Take 
the  temperature  of  the  water  in  each  pail. 

Now  place  the  hot  iron  in  one  pail  and  the  hot  water  in  the 
other  and  again  find  the  temperature  of  the  water  in  each  pail. 

Calculate  the  number  of  B.T.U.  given  up  by  the  hot  iron  and  by 
the  hot  water. 

FORM    OF   REPORT 

The  hot  iron  warmed ....  Ib.  of  water  from ....  °  F.  to  ....  °  F. 

.*.  the  iron  gave  up.  . .  .B.T.U. 
The  hot  water  warmed  ....  Ib.  of  water  from  ....  °  F.  to  ....  °  F. 

.'.  the  water  gave  up  ...  .B.T.U. 
....  at  212°  F.  contains  more  heat  than ....  at  212°  F. 

The  reason  for  this  is  that  water  has  a  greater  heat  capacity 
than  iron.  You  will  understand  this  better  when  you  have  deter- 
mined the  heat  capacity  or  specific  heat  of  iron  in  Experiment  18. 

Exercise  15.     Cooking  Utensils. 

Handles.  In  the  school  kitchen  name  five  cooking  utensils  with 
heat-resisting  handles.  Consult  page  108,  Physics  of  the  Household. 


LABORATORY  COURSE   IN  PHYSICS  43 

Conductivity.  Compare  the  heat  conductivity  of  a  copper  or 
aluminum  utensil  with  that  of  a  tin  utensil  of  the  same  size  and 
shape  as  follows : 

Heat  equal  weights  of  cold  water  in  each  vessel,  one  after  the 
other  on  the  same  fire,  for  equal  lengths  of  time,  and  find  the  change 
in  temperature  in  each.  Consult  page  119,  Physics  of  the  Household. 

Which  is  the  better  conductor  ? 

Size  of  bottom.  To  show  that  food  is  warmed  more  quickly  in  a 
utensil  with  a  large  bottom  than  in  one  with  a  small  bottom. 

Heat  equal  weights  of  cold  water  in  (i)  a  covered  saucepan  with 
a  large  bottom,  (2)  a  covered  tea  or  coffee  pot  with  a  small  bottom, 
one  after  the  other  on  the  same  fire,  and  find  the  time  required 
to  bring  the  water  to  the  boiling  point  in  each. 

Covers.  To  show  that  food  is  heated  more  quickly  in  covered 
than  in  uncovered  vessels. 

Heat  equal  weights  of  cold  water  (i)  in  a  covered  vessel  (2)  in 
the  same  vessel  uncovered,  on  the  same  fire,  and  find  the  time 
required  to  bring  the  water  to  the  boiling  point. 

Home  Exercise. 

Repeat  these  exercises  with  cooking  utensils  in  your  own  home 
and  make  a  written  report. 

Exercise  16.     Fireless  Cooker. 

Examine  the  school  fireless  cooker  and  make  a  diagram  illustrat- 
ing the  interior.  Consult  page  108,  Physics  of  the  Household. 

Test  the  cooker  as  follows :  Place  a  weighed  quantity  of  water 
(e.g.  10  Ib.)  in  one  of  the  kettles,  cover  and  heat  until  the  water 
boils  (2i2°F.).  Clamp  down  the  cover  and  place  the  kettle  in 
the  cooker.  Allow  the  cooker  to  stand  closed  for  a  certain  time 
(e.g.  12  hours),  find  the  temperature  of  the  water,  and  calculate 
the  number  of  B.T.U.  of  heat  which  have  escaped  through  the  sides 
of  the  cooker  per  hour. 

To  compare  fireless  cookers:  Make  the  above  test  with  two 
fireless  cookers  at  the  same  time.  The  better  cooker,  other  things 
being  equal,  is  the  one  which  loses  the  less  heat  per  hour. 


44  LABORATORY  COURSE  IN  PHYSICS 

Home  Exercise. 

Make  this  test  with  the  fireless  cooker  in  your  own  home  and 
make  a  written  report. 

Exercise  17.     Thermos  Bottle. 

Examine  the  school  thermos  bottle  and  make  a  diagram  illus- 
trating its  construction.  Consult  page  109,  Physics  of  the  House- 
hold. 

Test  it  as  follows :  Pour  into  the  bottle  a  definite  weight  (e.g. 
i  Ib.)  of  hot  water  and  find  its  temperature.  Allow  it  to  stand 
closed  for  a  known  time  (e.g.  12  hours),  find  the  temperature  of 
the  water  and  calculate  the  number  of  B.T.U.  of  heat  lost  by  the 
bottle  per  hour. 

Repeat  this  with  a  definite  weight  of  ice  water  and  calculate 
the  number  of  B.T.U.  of  heat  which  enter  the  bottle  per  hour. 

Do  you  find  that  a  thermos  bottle  keeps  a  thing  cool  better 
than  it  keeps  it  warm?  Explain  why.  Consult  page  no,  Physics 
of  the  Household. 

Home  Exercise. 

Make  this  test  with  your  own  thermos  bottle  and  make  a  written 
report. 

Exercise  18.     Ventilation. 

Examine  the  school  ventilation  system. 

Follow  the  path  of  the  air  from  the  point  at  which  it  enters  the 
school  to  the  point  at  which  it  leaves. 

Make  a  rough  diagram  representing  the  path  of  the  air. 

Home  Exercise. 

Make  a  diagram  of  the  ventilating  system  in  your  home,  if 
there  is  any. 

Make  a  diagram  showing  how  the  soil  pipe  in  your  home  is 
ventilated.  Consult  page  114,  Physics  of  the  Household. 

Make  a  written  report. 


LABORATORY   COURSE   IN   PHYSICS 


45 


Experiment  16.     Cooling  effect  of  ice  and  of  ice  water. 

To  show  that  equal  weights  of  ice  and  ice  water  have  different 
cooling  effects. 


FIG.  20.  Apparatus  used  to  show  that  equal  weights  of  ice  and  ice  water  have 
different  cooling  effects. 

Two  3-qt.  pails.  Balance,  Ib. 

Two  pails  and  strainer  for  ice  Fahrenheit  thermometer. 

water. 

Ice  cr  snow.  Burner  and  tripod. 

Method.  The  temperature  of  melting  ice  is  32°  F.  or  o°  C. ; 
the  temperature  of  ice  water  is  the  same.  We  wish  to  show  that 
equal  weights  of  these  substances  have  very  different  cooling 
effects. 

Make  some  ice  water  by  stirring  snow  or  ice  in  water,  and  when 
you  are  ready  to  use  the  ice  water  strain  it  through  a  cloth  to  re- 
move all  snow  or  ice. 

Weigh  an  empty  pail  and  add  to  it  a  certain  weight  of  water, 
say  2  Ib.  Cover  the  pail  and  heat  the  water  until  it  boils  vig- 
orously. Its  temperature  is  then  2i2°F.  Pour  into  this  i  Ib.  of 
ice  water,  and  take  the  temperature  after  stirring  for  about  i 


46  LABORATORY  COURSE  IN  PHYSICS 

minute.     Calculate  the  number  of  B.T.U.  the  ice  water  absorbed 
from  the  2  Ib.  of  water  at  212°  F. 

Repeat  this  experiment,  but  use  i  Ib.  of  dry  ice  instead  of  i  Ib. 
of  ice  water.  Calculate  the  number  of  B.T.U.  the  ice  absorbed 
from  the  2  Ib.  of  water  at  212°  F. 

FORM    OF   REPORT 

i  Ib.  of  ice  water  cooled  ....  Ib.  of  water  from  212°  F.  to  ....  °  F. 

.*.  the  i  Ib.  of  ice  water  absorbed.  . .  .B.T.U. 
i  Ib.  of  ice  cooled  ....  Ib.  of  water  from  212°  F.  to  .  . .  .°  F. 

.'.  the  i  Ib.  of  ice  absorbed B.T.U. 

....  has  a  greater  cooling  effect  than  the  same  weight  of  .... 

The  reason  for  this  is  that  144  B.T.U.  of  heat  are  required  to 
change  i  Ib.  of  ice  at  32°  F.  to  i  Ib.  of  water  at  32°  F.  You  will 
understand  this  better  after  you  have  determined  the  heat  of 
fusion  of  ice  in  Experiment  19. 


LABORATORY   COURSE  IN  PHYSICS 


47 


Experiment  17.     Heating  effect  of  steam  and  of  boiling  water. 
To  show  that  steam  and  boiling  water  have  very  different  heating 
effects. 


iviG.  21.     Apparatus  used  to  show  that  equal  weights  of  steam  and  boiling  water 
at  the  same  temperature  have  different  heating  effects. 


Two  3-qt.  pails. 
Balance,  Ib. 
Boiler. 


Fahrenheit  thermometer. 
Burner  and  tripod. 


Method.  Steam  under  atmospheric  pressure  has  a  temperature 
of  212°  F. ;  boiling  water  under  the  same  pressure  has  the  same 
temperature.  We  wish  to  show  that  equal  weights  of  steam  and 
boiling  water  have  different  heating  effects. 

Weigh  an  empty  pail  and  add  to  it  a  certain  weight  of  cold 
water,  say  4  Ib.  Take  the  temperature  of  the  water.  Balance  the 
pail  and  water  on  a  scales  and  pass  live  steam  into  the  water  until 


48  LABORATORY  COURSE   IN  PHYSICS 

a  certain  weight  of  steam  has  condensed  in  the  water,  say  \  Ib. 
Take  the  temperature  of  the  water  and  calculate  the  number  of 
B.T.U.  the  steam  gave  to  the  water. 

Repeat  this  experiment,  but  use  J  Ib.  of  boiling  water  instead  of 
J  Ib.  of  steam.  Calculate  the  number  of  B.T.U.  the  boiling  water 
gave  to  the  cold  water. 

FORM    OF   REPORT 

The Ib.  of  steam  warmed Ib.  of  water  from °F.to °F., 

/.  the  steam  gave  up  ...  .B.T.U. 

The  ....  Ib.  of  boiling  water  warmed  ....  Ib.  of  water  from  .  . .  .  °  F. 
to  .  . .  .°  F.,  .'.  the  boiling  water  gave  up  ....  B.T.U. 

A  given  weight  of has  a  greater  heating  effect  than  the  same 

weight  of 

The  reason  for  this  is  that  i  Ib.  of  steam  at  212°  F.  gives  up  966 
B.T.U.  of  heat  when  it  changes  to  i  Ib.  of  water  at  212°  F.  You 
will  understand  this  better  when  you  have  determined  the  latent 
heat  of  steam  in  Experiment  20. 


LABORATORY   COURSE  IN  PHYSICS 


49 


Experiment  18.     Specific  heat. 

To  find  the  specific  heat  of  iron,  lead  and  aluminium. 


o 


Apparatus  used  to  measure  the  specific  heat  of  solids. 


Boiler  with  dipper. 

Calorimeter. 

Two  thermometers. 


Balance. 

Burner  and  tripod. 
Lead  shot,  iron  nails  and  alu- 
minium pellets. 


If  we  measure  heat  in  B.T.U.  the  specific  heat  or  heat  capacity 
of  any  substance  may  be  defined  as  the  number  of  B.T.U.  required 
to  raise  the  temperature  of  i  Ib.  of  the  substance  i°  F.,  or  the  number 
of  B.T.U.  given  up  when  i  Ib.  of  the  substance  cools  i°  F. 

If  we  measure  heat  in  calories  the  specific  heat  or  heat  capacity 
of  any  substance  may  be  defined  as  the  number  of  calories  required 
to  raise  the  temperature  of  i  g.  of  the  substance  i°  C.  or  the  number 
of  calories  given  up  when  i  g.  of  the  substance  cools  i°  C.  ^ 

The  number  found  for  the  specific  heat  is  the  same,  no  matter 
which  system  of  measurement  we  use. 

In  the  previous  experiments  in  heat  we  have  measured  heat  in 


50  LABORATORY  COURSE  IN  PHYSICS 

B.T.U.  In  the  three  following  experiments  we  will  measure  heat 
in  calories,  in  order  to  obtain  experience  in  the  use  of  this  heat  unit. 

It  is  suggested  that  three  students,  or  three  pairs  of  students, 
make  this  experiment  side  by  side ;  the  first  student,  or  pair  of 
students,  using  iron,  the  second,  lead  and  the  third,  aluminium. 
Then  let  each  student,  or  pair  of  students,  copy  the  results  ob- 
tained by  the  other  two. 

We  propose  to  find  the  specific  heat  of  the  metals  by  the 
"method  of  mixtures."  This  method  is  as  follows:  A  known 
weight  of  the  metal  at  a  known  high  temperature  is  dropped  into  a 
known  weight  of  water  at  a  known  low  temperature  and  the  result- 
ing temperature  is  determined. 

Method  i.  Weigh  out  1000  g.  of  lead  shot,  or  250  g.  of  small 
iron  nails,  or  200  g.  of  aluminium  pellets.  Place  them  in  the  dip- 
per of  the  boiler,  Fig.  22  ;  insert  a  thermometer  bulb  to  about 
the  middle  and  cover  with  a  loose  fitting  cork.  Heat  until  the 
temperature  is  about  95°  C. 

While  the  metal  is  heating,  weigh  the  inner  vessel  of  the  calorim- 
eter and  add  to  it  200  g.  of  water  at  about  5°  or  10°  C.  below  the 
room  temperature.  When  you  find  that  the  metal  has  reached 
about  95°  C.,  read  the  temperature  of  the  water  to  .1°  C.  and  then 
add  the  metal  to  the  water  without  splashing.  Stir  the  contents 
for  one  minute  and  read  the  temperature  to  .1°  C. 

Calculate  the  specific  heat  of  the  metal  in  the  manner  illustrated 
in  the  following  example : 

One  thousand  g.  of  lead  at  95°  C.  placed  in  200  g.  of  water  at 
15°  C.  warms  the  water  to  26°  C.  What  is  the  specific  heat  of  the 
lead? 

If  there  has  been  neither  loss  nor  gain  of  heat,  in  the  whole 
apparatus,  we  know  that  the  heat  received  by  the  water  is  that 
given  up  by  the  lead.  We  can  calculate  the  amount  of  heat 
received  by  the  water  (since  the  heat  required  to  warm  i  g.  of 
water  i°  C  =  i  calorie),  and  this  is  the  amount  of  heat  given  up 
by  the  lead. 


LABORATORY  COURSE  IN  PHYSICS  51 

The  water  was  heated  from  15°  C.  to  26°  C.,  or  through  n°  C. ; 
therefore  the  water  received  from  the  lead  200  X  n  =  2200 
calories  of  heat. 

The  lead  cooled  from  95°  C.  to  26°  C.  or  through  69°  C.  We  can 
say  then : 

looo  g.  of  lead  in  cooling  69°  C.  gave  up  2200  calories. 


2200 


.'.  i  g.  of  lead  in  cooling  i°  C.  gave  up 

looo  X  69 

The  specific  heat  of  lead  =  .031  calorie. 


.031  calorie. 


NOTE  :  You  have  been  asked  to  make  this  experiment  in  order  that 
you  might  learn  the  common  method  of  obtaining  the  specific  heat  of  sub- 
stances. You  cannot  expect  your  results  to  be  accurate  because  you 
have  not  been  asked  to  take  into  account  the  heat  losses ;  for  example, 
the  heat  lost  in  warming  the  calorimeter,  the  heat  lost  in  transferring 
the  metal  from  the  boiler  to  the  calorimeter,  etc.  You  may  be  satisfied 
with  your  result  if  it  is  within  10  per  cent  of  the  correct  value. 


FORM    OF    REPORT 


IRON 

LEAD 

ALUMINIUM 

Weight  of  metal,  g.       
High  Temperature  of  metal,  °C.     .     . 
Low  Temperature  of  metal,  °C.  .     .     . 
Change  of  temperature  of  metal,  °C.   . 
Weight  of  water,  g  
High  Temperature  of  water,  °C.      .     . 
Low  Temperature  of  water,  °C.      .     . 
Change  of  temperature  of  water,  °C.  . 
Specific  heat    

Method  2.  If  the  laboratory  is  not  equipped  with  the  boiler 
shown  in  Fig.  22  and  with  a  calorimeter,  the  specific  heat  of  the 
metals  can  be  determined  with  the  apparatus  mentioned  below. 


52  LABORATORY  COURSE  IN  PHYSICS 

Two  3-qt.  pails.  Burner  and  tripod. 

Balance.  Iron,  lead,  and  aluminium. 

Thermometer. 

Attach  a  piece  of  cord  to  a  solid  piece  of  metal  and  weigh  it. 
Place  the  metal  in  a  pail  half  full  of  water  and  heat  it  until  the 
water  has  boiled  for  2  or  3  minutes. 

NOTE.  —  It  is  recommended  that  the  student  use  large  pieces  of  metal 
weighing  about  2000  g.  They  give  more  accurate  results  than  small 
pieces  because:  they  can  be  weighed  more  accurately  ;  and  they  produce 
greater  changes  in  temperature,  which  can  be  measured  more  accurately. 

With  a  measuring  cylinder  measure  out  2000  c.c.  (2000  g.)  of 
water  at  a  temperature  about  5°  C.  below  that  of  the  room,  and 
pour  it  into  a  3~qt.  pail. 

When  the  metal  is  warmed  (its  temperature  is  100°  C.)  take  the 
temperature  of  the  cold  water  to  .1°  C.  Place  the  hot  metal  in 
the  cold  water,  stir  for  one  minute  and  take  the  temperature  again 
to  .1°  C. 

Calculate  the  specific  heat  of  the  metal  as  illustrated  in  the 
following  example  : 

A  piece  of  iron  weighing  2000  g.  is  warmed  to  100°  C.  and  then 
placed  in  1500  g.  of  water  at  15°  C.  The  resulting  temperature 
is  25°  C.  What  is  the  specific  heat  of  iron? 

The  1500  g.  of  water  was  warmed  from  15°  C.  to  25°  C.  or 
through  10°  C.,  therefore  the  water  received  1500  X  10  =  15000 
calories  of  heat  from  the  hot  iron. 

The  2000  g.  of  iron  cooled  from  100°  C.  to  25°  C.  or  through 
75°  C.  We  can  say  then  : 

2000  g.  of  iron  in  cooling  75°  C.  gave  up  15000  calories  of  heat. 


.*.  i  g.  of  iron  in  cooling  i°  C.  gave  up  —          —  =  .1  calorie. 

2000  X  75 
Specific  heat  of  iron  =  .1. 

For  the  reasons  given  above  you  may  be  satisfied  with  your  results 
if  they  are  within  10  per  cent  of  the  true  value, 


LABORATORY  COURSE   IN  PHYSICS 
FORM    OF   REPORT 


53 


IRON 

LEAD 

ALUMINIUM 

Weight  of  metal  g    ,     . 

High  Temperature  of  metal,  °C.     ... 
Low  Temperature  of  metal,  °C.      .     .    „ 
Change  of  temperature  of  metal,  °C.   .     . 
Weight  of  water,  g  . 
High  Temperature  of  water,  °C.      ... 
Low  Temperature  of  water,  °C.  .     . 
Change  of  temperature  of  water,  °C.    .     . 
Specific  heat                        .     .     .     .     .     . 

(Look  up  table  of  specific  heats,  page  138) 


54 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  19.     Latent  heat  of  fusion  of  ice. 

To  find  the  number  of  calories  required  to  change  i  g.  of  ice  at 
o°  C.  to  i  g.  of  water  at  o°  C.,  that  is,  to  find  the  latent  heat  of 
fusion  of  ice. 


FIG.   23.     Apparatus  used  to  measure  the  latent  heat  of  fusion  of  ice. 


Calorimeter. 
Thermometer. 


Balance. 

Ice. 

Towel. 


Method  i.  Weigh  the  inside  vessel  of  the  calorimeter  and  add 
to  it  200  g.  of  water  at  about  10°  C.  above  room  temperature. 

Break  some  clear  ice  into  lumps  about  i  in.  in  diameter  and 
weigh  out  roughly  about  50  g.  of  these  lumps. 

Take  the  temperature  of  the  water  to  .1°  C.  Dry  each  lump 
with  a  towel  and  add  it  to  the  water.  Stir  until  the  ice  is  melted 
and  read  the  temperature  of  the  water  to  .1°  C. 

Weigh  the  inside  vessel  of  the  calorimeter  again  to  find  the 
weight  of  the  ice  used. 

If  there  has  been  neither  loss  nor  gain  of  heat,  the  heat  given  uj 
by  the  water  is  that  taken  up  by  the  ice,  and  since  we  can  calculate 
the  amount  of  heat  given  up  by  the  water  we  know  the  amount 


LABORATORY   COURSE   IN   PHYSICS  55 

taken  up  by  the  ice.  It  will  be  noticed  that  the  ice  takes  up  heat 
in  two  ways :  first,  when  it  changes  from  ice  at  o°  C.  to  water  at 
o°  C.,  and  second,  when  the  resulting  ice  water  is  warmed  from 
o°  C.  to  the  final  temperature. 

Calculate  the  latent  heat  of  fusion  of  the  ice  as  illustrated  in 
this  example : 

200  g.  of  water  at  35°  C.  is  cooled  to  12°  C.  by  50  g.  of  ice. 
What  is  the  latent  heat  of  the  ice? 

The  200  g.  of  water  is  cooled  from  35°  C.  to  12°  C.  or  through 
23°  C. ;  therefore  the  water  gave  up  200  X  23  =  4600  calories. 

The  50  g.  of  ice  at  o°  C.  was  changed  to  50  g.  of  water  at  o°  C. 
and  then  the  50  g.  of  water  was  warmed  from  o°  to  12°  C.  This 
warming  of  the  50  g.  of  water  from  o°  C.  to  12°  C.  required  50  X 
12  =  600  calories. 

The  total  heat  received  by  the  ice  was  4600  calories,  but  600 
calories  were  required  to  warm  the  ice  water.  The  difference, 
4600  —  600  =  4000  calories,  was  used  to  melt  50  g.  of  ice ;  there- 
fore 4000-^  50  =  80  calories  is  the  amount  of  heat  required  to  melt 
i  g.  of  ice. 

The  latent  heat  of  fusion  of  ice  =  80  calories. 

NOTE.  —  You  have  been  asked  to  make  this  experiment  in  order  that 
you  might  learn  the  common  method  of  finding  the  latent  heat  of  fusion 
of  ice.  You  cannot  expect  your  results  to  be  accurate  because  you  have 
not  been  asked  to  take  account  of  the  heat  gains ;  for  example,  the  heat 
gained  by  the  cooling  of  the  calorimeter,  and  the  heat  gained  because 
some  water  (melted  ice)  was  added  with  the  ice.  You  may  be  satisfied 
if  your  results  are  within  10  per  cent  of  the  correct  value. 


FORM    OF   REPORT 

Weight  of  calorimeter  =   . . .  .  g.   Temp,  of  water,  beginning  =  . . .  .  °C. 
Weight  of  water  =    . . .  .  g.   Temp,  of  water,  end  =  . . .  .  °C. 

Weight  of  ice  =    .  . .  .  g. 

The  latent  heat  of  fusion  pf  ice  = calories  per  gram. 


56  LABORATORY   COURSE   IN  PHYSICS 

When  we  measure  heat  in  calories  as  above,  the  latent  heat  of 
fusion  of  ice  is  80  calories  per  gram,  but  when  we  measure  heat  in 
B.T.U.  the  latent  heat  of  fusion  of  ice  is  80  X  |  =  144  B.T.U.  per 
pound.  The  reason  for  this  is  that  the  Fahrenheit  degree  is  equal 
to  f  of  a  centigrade  degree  and  therefore  there  are  f  as  many  in  a 
given  change  of  temperature. 

Method  2.  If  the  laboratory  is  not  equipped  with  a  calorimeter, 
the  latent  heat  of  fusion  of  ice  can  be  determined  with  the  apparatus 
given  here. 

Pail,  3-qt.  Thermometer. 

Measuring  cylinder  1000  c.c.  Ice. 

Measure  very  carefully  2000  c.c.  (2000  g.)  of  cold  water,  then 
pour  it  into  a  3-qt.  pail  and  warm  it  to  about  35°  C. 

Break  clear  ice  into  lumps  about  the  size  of  an  egg  and  weigh 
out  very  roughly  500  g.  of  it. 

Take  the  temperature  of  the  water  to  .1°  C. ;  dry  the  ice  with 
a  towel  and  place  it  in  the  water ;  stir  until  the  ice  is  melted  and 
take  the  temperature  to  .1°  C. 

Measure  the  water  again  and  subtract  2000  c.c.  to  find  the 
weight  of  ice  added. 

Calculate  the  latent  heat  of  ice  as  shown  in  this  example : 

Two  thousand  g.  of  water  at  32.5°  C.  is  cooled  to  10°  C.  by  500 g 
of  ice.  What  is  the  latent  heat  of  ice  ? 

The  2000  g.  of  water  was  cooled  from  32.5  to  10°,  therefore  it 
gave  up  2000  X  22.5  =  45000  calories  of  heat  to  the  ice. 

The  500  g.  of  ice  at  o°  C.  was  changed  to  500  g.  of  water  at 
o°  C.  and  then  was  warmed  to  10°  C.  To  warm  500  g.  of  water 
from  o°  C.  to  10°  C.  required  500  X  10  =  5000  calories  of  heat. 

The  ice  absorbed  in  all  45000  calories  of  heat,  but  of  this  5000 
calories  were  required  to  warm  the  500  g.  of  water  from  o°  to  ioc 
therefore    the    difference,    45000  —  5000  =  40000    calories,   was 
required  to  change  500  g.  of  ice  at  o°  C.  to  500  g.  of  water  at  o°  C. 
We  can  say  then : 


LABORATORY   COURSE   IN   PHYSICS  57 

To  melt  500  g.  of  ice  required  40000  calories. 


.-.to  melt  i  g.  of  ice  required  ^^  =  80  calories. 

500 

The  latent  heat  of  ice  =  80  calories. 

FORM    OF   REPORT 

Weight  of  water  =    g.     Temp,  of  water,  end  = °  C. 

Temp,  of  water,  beginning  =    . ... ,.°  C.     Weight  of  ice  =  .  . .  .     g. 

Latent  heat  of  ice  = 

As  stated  above,  when  we  measure  heat  in  calories,  the  latent 
heat  of  ice  is  80-  calories  per  gram,  but  when  we  measure  heat  in 
B.T.U.  it  is  80  X  $•  =  144  B.T.U.  per  pound. 

Exercise  19.     Refrigerators. 

Examine  the  school  refrigerator  and  make  a  diagram  illustrating 
the  interior.  Consult  page  103,  Physics  of  the  Household. 

Test  it  as  follows :  Empty  the  pan  beneath  the  refrigerator, 
close  the  refrigerator  for  10  or  12  hours,  and  find  the  weight  of 
water  in  the  pan.  Calculate  the  number  of  B.T.U.  of  heat  which 
entered  the  refrigerator  per  hour,  using  the  fact  that  144  B.T.U. 
of  heat  are  required  to  change  i  Ib.  of  ice  at  32°  F.  to  i  Ib.  of  water 
at  32°  F.  Consult  page  135,  Physics  of  the  Household. 

To  Compare  Refrigerators. 

Make  the  above  test  with  two  refrigerators  at  the  same  time. 

Home  Exercise. 

Repeat  this  test  with  the  refrigerator  in  your  own  home  and  make 
a  written  report. 

Exercise  20.     Artificial  Refrigeration. 

As  a  class  visit  a  refrigeration  plant  and  learn  all  you  can  about 
it.  Locate  the  compressor,  condenser,  evaporator,  and  the  brine 
circulating  system. 

Make  a  rough  diagram  illustrating  the  system.  Consult  page 
138,  Physics  of  the  Household. 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  20.     Latent  heat  of  steam. 

To  find  the  number  of  calories  of  heat  given  up  when  i  g.  of 
steam  at  100°  C.  changes  to  i  g.  of  water  at  100°  C. ;  that  is,  to 
find  the  latent  heat  of  steam. 


Q, 


FIG.  24.     Apparatus  used  to  measure  the  latent  heat  of  steam. 


Boiler. 
Water  trap. 
Calorimeter. 


Tripod  and  burner. 
Thermometer. 
Balance  and  weights. 


Method  i.  Fill  the  boiler  about  half  full  of  water  and  start  it 
heating. 

Weigh  the  inner  vessel  of  the  calorimeter.  Make  some  ice 
water  in  a  pail,  strain  it  through  a  cloth  to  separate  the  ice,  and 
weigh  out  about  200  g.  of  the  ice  water  in  the  calorimeter. 

When  the  steam  is  issuing  freely  from  the  boiler,  attach  the 
water  trap ;  take  the  temperature  of  the  water  in  the  calorimeter 
to  .1°  C.  (you  will  find  the  ice  water  has  warmed  to  about  5°  C.)j 


LABORATORY  COURSE  IN  PHYSICS  59 

and  then  place  the  delivery  tube  from  the  water  trap  about  2  cm. 
below  the  surface  of  the  water. 

Continue  to  pass  steam  into  the  water  until  the  temperature  is 
about  35°  C. 

Remove  the  delivery  tube  and  take  the  temperature  of  the 
water  to  .1°  C. 

Weigh  the  calorimeter  and  water  again  to  determine  the  weight 
of  steam  condensed  in  the  water. 

If  there  has  been  neither  gain  nor  loss  of  heat,  we  know  that  the 
heat  taken  up  by  the  water  is  that  given  up  by  the  steam  when  it 
condenses  from  steam  at  100°  C.  to  water  at  100°  C.  and  then 
cools  to  the  final  temperature.  We  can  calculate  the  amount  of 
heat  taken  up  by  the  water,  and  this  is  the  amount  given  up  by 
the  steam. 

Calculate  the  latent  heat  of  steam  as  shown  in  this  example : 

200  g.  of  water  at  5°  C.  is  warmed  to  35°  C.  by  10  g.  of  steam. 
What  is  the  latent  heat  of  steam? 

The  200  g.  of  water  is  warmed  from  5°  C.  to  35°  C.  or  through 
30°  C.,  therefore  the  water  receives  from  the  steam  200  X  30  = 
6000  calories  of  heat. 

The  10  g.  of  steam  at  100°  C.  changed  to  10  g.  of  water  at 
100°  C.  and  then  cooled  to  35°  C.  or  through  65°  C.  When  the 
10  g.  of  water  at  100°  C.  cooled  through  65°  C.  it  gave  to  the 
water  10  X  65  =  650  calories  of  heat. 

The  10  g.  of  steam  gave  up  6000  calories  in  all,  but  650  were 
given  up  in  cooling;  therefore  6000  —  650  =  5350  calories  were 
given  up  in  changing  from  steam  at  100°  C.  to  water  at  100°  C. 

We  can  say  then : 

10.  g.  of  steam  gave  up  5350  calories  in  condensing. 

.'.  i  g.  of  steam  gave  up  &S°  =  535  calories. 
10 

The  latent  heat  of  steam  is  535  calories  per  g. 
(Correct  value,  537  calories.) 


60  LABORATORY  COURSE  IN  PHYSICS 

NOTE. — You  have  made  this  experiment  in  order  to  learn  the  common 
method  of  determining  the  latent  heat  of  steam.  You  cannot  expect 
your  results  to  be  correct  because  you  have  not  been  asked  to  take  into 
account  the  heat  losses;  for  example,  the  heat  lost  in  warming  the 
calorimeter,  the  heat  lost  by  the  condensation  of  the  steam  before  it 
enters  the  water,  etc.  You  may  be  satisfied  with  your  results  if  they 
are  within  10  per  cent  of  the  true  value. 

FORM    OF   REPORT 

Weight  of  calorimeter         =  .  . .  .  g.     Temperature    of   water,  end 

=  .  ...°C. 
Weight  of  calorimeter         +    water     Weight  of  calorimeter  +  water  + 

=  .  . .  .  g.         steam  =  .  . .  .  g. 

Weight  of  water  =  .  . .  .  g.     Weight  of  steam  =  .  . .  .  g. 

Temperature  of  water,  beginning  =  .  . .  .  °  C. 

Latent  heat  of  steam  =  .  . .  .  calories  per  gram. 

When  we  measure  heat  in  calories  as  above,  the  latent  heat  of 
steam  is  537  calories  per  g.,  but  when  we  measure  heat  in  B.T.U. 
the  latent  heat  of  steam  is  537  X  f  =  966  B.T.U.  per  pound. 
The  reason  for  this  is  that  one  Fahrenheit  degree  is  equal  to  f  of 
a  centigrade  degree  and  therefore  there  are  -|  as  many  in  any  given 
change  of  temperature. 

Method  2.  If  the  laboratory  is  not  equipped  with  a  boiler  (Fig. 
24)  and  a  calorimeter,  the  latent  heat  of  steam  can  be  found  with 
the  apparatus  listed  below. 

Sirup  can  boiler.  Balance  and  weights. 

Burner  and  tripod.  Thermometer. 

Water  trap.  Two  3-qt.  pails. 

Start  water  heating  in  the  boiler. 

In  a  3-qt.  pail  cool  some  water  with  snow  or  ice. 

Attach  the  counterpoise  weight  to  the  left  arm  of  the  balance, 
attach  the  second  3-qt.  pail  to  this  and  weigh  the  pail,  then  strain 
into  the  pail  1000  g.  of  ice  water. 


LABORATORY   COURSE   IN   PHYSICS 


6l 


FIG.  25.     Simpler  apparatus  used  to  measure  the  latent  heat  of  steam. 

Take  the  temperature  of  the  water  to  .1°  C.  (it  will  be  at  about 
5°  C.)  and  pass  steam  into  it  until  its  temperature  is  about  35°  C. 
Keep  the  delivery  tube  of  the  water  trap  about  2  cm.  below  the 
surface  and  stir  the  water  continuously. 

Take  the  temperature  of  the  water  to  .1°  C.  and  then  weigh 
again  to  find  the  weight  of  steam. 

Calculate  the  latent  heat  of  steam  as  shown  in  the  following 
example  : 

1000  g.  of  water  at  5°  C.  is  warmed  to  35°  by  50  g.  of  steam. 
What  is  the  latent  heat  of  steam? 

The  1000  g.  of  water  is  warmed  from  5°  to  35°  or  through  30°, 
therefore  the  water  received  1000  X  30  =  30000  calories  of  heat 
from  the  steam. 

The  50  g.  of  steam  at  100°  C.  changed  to  water  at  100°  C.  and 
then  cooled  to  35°  C.  When  the  50  g.  of  water  cooled  from  100°  C. 
to  35°  C.  or  through  65°,  it  gave  up  65  X  50  =  3250  calories  of 
heat. 

The  total  heat  from  the  steam  was  30000  calories,  but  of  this, 


62  LABORATORY   COURSE   IN  PHYSICS 

3250  calories  came  from  the  steam  water;  the  difference,  30000  — 
3250  =  26750  calories,  was  given  up  by  50  g.  of  steam  at  100°  C. 
when  it  condensed  to  water  at  100°  C. 

We  can  say  then : 

50  g.  steam  in  condensing  gave  26 7  50  calories. 

.'.  i  g.  steam  in  condensing  gave      ^°  =  535  calories. 

5o 

The  latent  heat  of  steam  is  535  calories. 
(The  true  value  is  537  calories.) 

FORM    OF   REPORT 

Weight  of  calorimeter         =  .  . .  .  g.     Temperature   of   water,    end 

=  .  ...°C. 

Weight  of  calorimeter         +  water    Weight  of  calorimeter  -f-  water  -f 
=  .  . .  .  g.         steam  =  .  . .  .  g. 

Weight  of  water  =  .  . .  .  g.    Weight  of  steam  = g. 

Temperature  of  water,   beginning 

=  .  . .  .  °  C. 
Latent  heat  of  steam  =  .  . .  .  calories  per  gram. 

As  explained  above,  when  we  measure  heat  in  calories  the  latent 
heat  of  steam  is  537  calories  per  g.,  but  when  we  measure  heat 
in  B.T.U.  the  latent  heat  of  steam  is  537  X  f  =  966  B.T.U.  per  Ib. 

Exercise  21.     Fuels. 

Find  the  average  weight  of  fuel  used  in  the  school  range  per  day 
and  calculate  the  .cost  per  day.  Consult  pages  152,  153,  Physics 
of  the  Household. 

Find  the  average  amount  of  fuel  used  to  heat  the  school  per  day 
and  calculate  the  cost  per  day. 

Home  Exercise. 

Repeat  this  exercise  in  your  own  home  and  make  a  written 
report. 

NOTE.  —  If  you  use  coal,  find  the  average  weight  of  a  scuttle  of  coal 
and  the  number  of  scuttles  used  per  day  and  calculate  from  these  the 


LABORATORY  COURSE  IN  PHYSICS  63 

cost  of  the  range  fuel  per  day.  Also  find  the  average  weight  of  a  shovel- 
ful of  coal  and  the  average  number  used  in  the  furnace  per  day,  then  cal- 
ilate  from  these  the  cost  of  the  furnace  fuel  per  day. 

If  you  use  petroleum  as  fuel,  calculate  the  cost  per  day  from  the  price 
jr  gallon  and  the  average  number  of  days  a  gallon  lasts. 

If  you  use  gas  as  fuel,  calculate  the  cost  per  day  from  the  number  of 
:ubic  feet  used  per  day  and  the  price  per  cubic  foot. 

If  you  use  wood  as  fuel,  consider  i  cord  of  hard  wood  to  weigh  4000 
Ib.  and  i  cord  of  pine  2000  lb.,  and  calculate  the  cost  from  the  weight 

wood  used  per  day. 


LABORATORY  COURSE  IN  PHYSICS 


ELECTRICITY  AND  MAGNETISM 

Experiment  21.     The  simple  cell. 

To  show  that  an  electric  current  is  produced  when  two  different 

metals  are  placed  in  a  solution  of  a  salt,  or  of  an  acid,  or  of  a  base. 


Two  tumblers. 

Strip  holder. 

Salt. 

Acid  solution. 

Sticks  of  KOH  or  NaOH. 


Galvanometer. 

Strips  of  copper,  zinc,  lead, 

aluminium,  iron,  etc. 
Rod  of  carbon. 


Method.  Water.  Use  strips  of  metal  about  4  in.  long  and  i  in. 
wide. 

Fill  the  tumbler  f  full  of  water. 

Use  copper  and  zinc,  connect  with  the  galvanometer  and  place 
the  strips  in  water. 

Repeat  with  the  carbon  rod  and  zinc  strip. 

Do  you  notice  a  deflection  of  the  galvanometer  needle  ?  (If  the 
galvanometer  is  sufficiently  sensitive  you  will  notice  a  small  de- 
flection. A  galvanometer  is  used  to  detect  and  measure  an  electric 
current.) 

Salt  solution.  Lift  the  strips  out  of  the  water  and  stir  a  small 
handful  of  table  salt  in  the  water. 

Try  the  metals  in  pairs. 

Do  two  different  metals  in  the  salt  solution  produce  a  current? 
Do  you  notice  that  the  current  is  sometimes  in  one  direction  and 
sometimes  in  the  other? 

Use  the  carbon  rod  and  the  zinc  strip,  and  remember  the  direc- 
tion in  which  the  needle  of  the  galvanometer  turns.  In  any  elec- 
tric cell  there  are  two  different  metals,  and  one  metal  is  less  readily 
dissolved  than  the  other.  The  metal  less  readily  dissolved  i< 
charged  with  positive  electricity  and  is  called  the  positive  pole ; 
the  other  is  charged  with  negative  electricity  and  is  called  the 


66  LABORATORY   COURSE  IN  PHYSICS 

negative  pole.  The  electric  current  flows  through  the  wire  from 
the  positive  pole  to  the  negative  pole. 

In  the  case  of  the  carbon  and  zinc  above,  the  current  flows 
through  the  wire  from  the  carbon  to  the  zinc.  If  any  other  pair 
of  metals  turns  the  needle  in  the  same  direction  as  the  carbon  and 
zinc,  you  will  know  that  the  metal  taking  the  place  of  the  carbon 
is  the  positive  pole  and  that  taking  the  place  of  the  zinc  is  the 
negative  pole. 

Acid  solution.  You  will  find  on  the  table  a  large  bottle  of 
dilute  sulphuric  acid  (i  part  acid  poured  into  60  parts  water). 
Empty  out  the  salt  solution,  rinse  and  fill  the  tumbler  f  full  of 
the  acid  solution. 

Try  the  metals  in  pairs.  (Be  careful  not  to  get  acid  on  your 
clothes.  It  would  be  well  to  have  an  empty  tumbler  at  hand  to 
hold  the  strips  after  you  have  used  them.) 

Do  two  different  metals  in  the  acid  solution  produce  a  current? 

Solution  of  a  base.  Pour  the  acid  solution  back  into  the  large 
bottle,  rinse  the  tumblers  and  strips. 

Fill  the  tumbler  f  full  of  water  and  dissolve  in  it  a  stick  of  KOH 
or  NaOH  about  i  inch  long. 

Do  two  different  metals  in  a  solution  of  a  base  produce  an  electric 
current  ? 

Empty  out  the  solution  and  rinse  the  tumblers  and  strips. 

You  have  shown  that  when  two  different  metals  are  placed  in  a 
solution  of  a  salt,  acid,  or  base,  a  current  is  produced  in  the  wire 
joining  the  metals.  It  has  been  found  by  experiment  that  when 
any  two  different  metals  are  placed  in  a  solution  of  any  salt,  acid, 
or  base,  a  current  is  produced  in  the  wire  joining  the  metals. 


LABORATORY  COURSE  IN  PHYSICS  67 

Experiment  22.     Magnets. 

To  study  the  properties  of  permanent  magnets. 


FIG.  27.     Apparatus  used  to  illustrate  the  properties  of  permanent  magnets. 

• 

Two  U  magnets.  Bunsen  burner. 

Bar  magnet.  Pliers. 

Two  sewing  needles.  Bar  of  soft  iron. 

Iron  filings.  Thread. 
Pieces  of  iron,  brass,  le.ad,  aluminium,  wood,  etc. 

Method.  How  does  a  magnet  point?  Suspend  a  magnet,  by 
means  of  a  string  attached  at  the  middle  or  by  means  of  a  stirrup, 
in  such  a  way  that  it  is  free  to  turn.  Choose  a  place  where  there 
is  no  iron  within  3  or  4  feet.  After  the  string  has  untwisted  for 
an  hour  observe  the  direction  of  the  magnet  poles.  Do  the  poles 
point  north  and  south? 

What  substances  does  a  magnet  attract?  Apply  a  strong 
magnet  to  pieces  of  iron,  steel,  brass,  lead,  aluminium,  wood,  etc. 
What  substances  does  a  magnet  attract? 

Which  poles  attract  each  other  and  which  repel?  Apply  the 
N  pole  of  one  magnet  to  the  N  and  S  poles  of  another.  Repeat 
with  the  S  pole.  Which  poles  of  two  magnets  attract  each  other  ? 
Which  repel? 


68  LABORATORY   COURSE   IN   PHYSICS 

To  make  a  permanent  magnet.  Use  an  ordinary  sewing  needle 
about  i^  in.  long,  stroke  it  2  or  3  times  from  the  eye  to  the  point 
with  the  N  pole  of  a  magnet.  Does  the  needle  pick  up  iron  filings, 
that  is,  is  it  a  magnet  ?  Find  the  poles  of  the  needle  as  follows : 
Place  the  needle  on  the  table  and  move  the  N  pole  of  the  magnet 
along  the  table  towards  it  in  a  line  at  right  angles  to  the  needle 
at  the  middle.  Which  end  of  the  needle  is  a  N  pole  ?  The  point 
is  the  end  last  touched  by  the  N  pole ;  is  it  a  N  pole  or  a  S  pole? 

Stroke  the  same  needle  3  or  4  times  from  eye  to  point  with  the 
S  pole  of  a  magnet.  Repeat  the  test  with  N  and  S  pole  of  the 
magnet.  Is  the  end  last  touched  by  the  S  pole  a  N  or  a  S  pole? 

Have  you  reversed  the  poles  of  the  needle  ? 

Magnetic  induction.  Place  the  needle,  used  above,  on  the  table 
and  remember  which  end  is  the  N  pole  and  which  the  S  (test  with 
a  magnet  if  necessary).  Place  a  piece  of  soft  iron  in  front  of  the 
N  pole  of  a  magnet  and  about  J  in.  from  it.  Move  the  soft  iron 
and  magnet  toward  the  needle  in  a  line  at  right  angles  to  the  needle 
as  above. 

Does  the  soft  iron  become  a  magnet?  Which  pole,  N  or  S, 
does  the  end  of  the  soft  iron  farthest  from  the  N  pole  of  the  magnet 
become  ?  Which  pole  does  the  nearer  end  become  ? 

Place  the  soft  iron  J  in.  in  front  or  the  S  pole  of  the  magnet  and 
repeat  the  experiment.  Which  pole,  N  or  S,  does  the  end  of  the 
soft  iron  farthest  from  the  S  pole  of  the  magnet  become  ?  Which 
pole  does  the  nearer  end  become  ? 

The  effect  of  breaking  a  magnet.  Use  the  needle  you  stroked 
with  the  poles  of  the  magnet.  Cover  it  with  iron  filings  and  lift 
it  out.  Are  the  filings  most  numerous  at  the  ends? 

Test  with  a  magnet  to  make  sure  which  end  of  the  needle  is  the 
N  pole  and  which  the  S  pole,  then  break  the  needle  into  two 
pieces.  Cover  each  piece  with  filings.  Are  new  poles  formed? 

Place  the  pieces  on  the  table  and  test  with  a  magnet  to  determine 
which  of  the  new  poles  is  N  and  which  S. 

Have  two  new  magnets  been  made  by  breaking  the  needle  ? 


LABORATORY   COURSE  IN  PHYSICS  69 

Break  one  of  the  pieces  again.  Are  two  more  new  magnets 
made? 

The  effect  of  heating  a  magnet.  Magnetize  the  second  needle 
strongly  by  stroking  it  3  or  4  times  with  the  N  pole  of  the  magnet. 
Dip  the  needle  in  iron  filings.  Is  it  strongly  magnetized? 

Hold  the  needle  with  a  pair  of  pliers  and  heat  the  ends  red  hot 
in  turn.  Place  the  needle  in  filings.  Is  it  a  magnet? 

Remagnetize  the  needle  and  repeat. 

Read  up  in  the  text  book  on  the  theory  that  each  molecule  of 
iron  or  steel  is  a  magnet.  Do  these  experiments  support  this 
theory  ? 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  23.     Magnetic  fields. 

To  trace  the  magnetic  lines  of  force  in  magnetic  fields. 


FIG.  28.     Apparatus  used  to  trace  the  magnetic  lines  of  force  in  magnetic  fields. 


Bar  magnet. 

T* wo  horseshoe  magnets. 

Glass  plate. 


Soft  iron  bar. 

Iron  filings  in  sifter. 

Small  compass. 


Method.  Place  a  bar  magnet  on  the  table  and  place  over  it  a 
sheet  of  glass.  Sift  iron  filings  (from  a  cheesecloth  fbag  or  from  a 
sifter)  evenly  over  the  glass.  Tap  the  glass  until  the  filings  are 
in  curved  lines.  The  filings  trace  out  magnetic  lines  of  force  in 
the  plane  of  the  glass. 

Place  a  small  compass  at  different  positions  on  the  glass  where 
the  lines  are  distinct.  Does  the  needle  take  a  position  parallel 
to  the  lines  of  force  in  each  position  ? 

A  magnetic  line  of  force  is  assumed  to  run  from  N  to  S  outside 
the  magnet  and  from  S  to  N  inside  the  magnet.  Does  the  N  pole 
of  the  compass  point  in  the  direction  the  lines  of  force  run  ? 

Horseshoe  magnet.  Repeat  this  experiment,  but  use  a  horse- 
shoe magnet  instead  of  a  bar  magnet. 


LABORATORY  COURSE  IN  PHYSICS  71 

Does  the  N  pole  of  the  compass  point  in  the  direction  the  lines 
of  force  run  ? 

Magnetic  induction.  Place  a  bar  of  soft  iron  (J  in.  in  diameter 
or  larger  and  about  2  in.  longer  than  the  poles  of  the  magnet  are 
apart)  across  the  poles  of  the  horseshoe  magnet  but  about  2  in. 
from  the  poles.  Sift  filings  over  the  glass  and  find  the  magnetic 
lines  of  force  as  above.  Do  you  notice  that  many  magnetic  lines 
of  force  run  from  the  N  pole  to  one  part  of  the  soft  iron  bar  and 
then  from  the  other  part  of  the  bar  back  to  the  S  pole  ?  Also  that 
there  are  no  magnetic  lines  of  force  beyond  the  soft  iron  bar? 

This  shows  that  the  lines  pass  through  iron  more  readily  than 
they  do  through  air. 

Two  magnets.  Place  two  horseshoe  magnets  2  in.  apart  on  the 
table  with  the  S  pole  of  the  first  opposite  the  N  pole  of  the  second 
and  N  pole  of  first  opposite  S  pole  of  second.  Trace  the  magnetic 
line  of  force  with  filings  as  above.  Do  you  notice  that  the  lines 
of  force  run  from  each  N  pole  to  both  S  poles  ? 

Place  the  two  horseshoe  magnets  2  in.  apart  on  the  table  with 
N  pole  of  first  opposite  N  pole  of  second  and  S  pole  of  first  opposite 
S  pole  of  second.  Trace  the  lines  of  force  with  iron  filings  as  above. 

Do  you  notice  that  the  magnetic  lines  of  force  starting  at  the 
N  pole  of  each  magnet  return  to  the  S  pole  of  the  same  magnet 
and  that  the  magnetic  lines  of  force  of  one  magnet  appear  to 
repel  those  of  the  other? 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  24.     Magnetic  effect  of  an  electric  current. 
To  study  the  magnetic  effect  of  an  electric  current,  the  electro- 
magnet, and  the  solenoid. 


FIG.  29.     Apparatus  used  to  illustrate:  the  magnetic  effect  of  an  electric  current, 
the  electromagnet,  and  the  solenoid. 


Dry  cell. 

Compass. 
Iron  filings. 


Soft  iron  bar. 
Soft  iron  horseshoe. 
Two  pieces  of  insulated  wire  2  feet 
long  and  one  piece  8  feet  long. 


Method.  Attach  wires  2  feet  long  to  the  poles  of  a  dry  cell. 
Place  a  compass  on  the  table  and  lay  one  wire  over  the  compass 
parallel  to  the  needle.  Bring  the  bare  ends  of  the  wires  together 
for  an  instant. 

NOTE.  —  When  using  a  dry  cell  do  not  allow  the  current  to  run  longer 
than  10  or  20  seconds  at  one  time. 

Has  the  electric  current  a  magnetic  effect,  that  is,  does  it  make 
the  compass  needle  move  ? 

Test  the  following  rule,  which  enables  us  to  determine  the  re- 
lation between  the  direction  of  the  current  and  the  direction  of 
the  magnetic  lines  of  force  produced  by  the  current. 


LABORATORY   COURSE  IN   PHYSICS  73 

RULE  :  Grasp  the  wire  in  the  right  hand  with  the  extended  thumb 
pointing  in  the  direction  the  current  flows  ;  the  fingers  then  point  in 
the  direction  of  the  magnetic  lines  of  force  about  the  wire. 

To  test  this  rule  you  must  remember : 

(1)  That  the  electric  current  is  assumed  to  flow  in  the  direction 
the  +  electricity  moves ;  in  this  case  from  the  carbon  pole  of  the 
dry  cell,  through  the  wire,  to  the  zinc  pole. 

(2)  That  a  magnetic  needle  places  itself  parallel  to  the  lines  of 
force  of  a  magnetic  field  with  its  N  pole  in  the  direction  the  lines  run. 

Test  the  rule  as  follows : 

Place  the  wire  from  the  carbon  pole  over  the  compass,  parallel 
to  the  needle : 

(1)  With  the  current  flowing  from  N  to  S. 

(2)  With  the  current  flowing  from  S  to  N. 

Place  the  wire  from  the  carbon  pole  under  the  compass,  parallel 
to  the  needle. 

(1)  With  the  current  flowing  from  N  to  S. 

(2)  With  the  current  flowing  from  S  to  N. 

Does  the  rule  give  you  the  direction  of  the  magnetic  lines  of  force 
in  each  case,  that  is,  the  direction  the  N  pole  turns? 

Fold  one  wire  and  pass  the  current  over  the  needle  in  both 
directions  at  once ;  be  sure  that  the  folded  wire  is  exactly  parallel 
to  the  needle.  Is  the  effect  zero?  That  is,  does  the  magnetic 
field  about  one  fold  of  the  wire  exactly  counteract  the  magnetic 
field  about  the  other? 

Pass  the  current  over  and  under  the  needle.  Is  the  effect 
greater  than  when  the  current  passes  only  in  one  direction  ?  Apply 
the  rule  to  each  part  of  the  current  to  determine  whether  the 
magnetic  fields  of  each  part  of  the  current  tend  to  turn  the  needle 
in  the  same  direction. 

Loop  the  wire  3  or  4  times  about  the  compass  parallel  to  the 
needle.  Is  the  effect  of  the  current  still  greater? 

To  determine  the  direction  of  an  unknown  current.  Hide  the 
dry  cell  behind  a  book  and  bring  the  wires  out  from  under  the 


74  LABORATORY  COURSE  IN  PHYSICS 

book.  Notice  the  direction  the  current  moves  the  needle  and 
use  the  rule  to  determine  the  direction  the  current  is  flowing  in 
the  wire.  Practice  this  a  number  of  times  and  check  your  results 
by  following  the  wire  back  to  the  cell. 

ELECTROMAGNET 

To  make  an  electromagnet,  wind  a  bar  of  soft  iron  with  50  turns 
of  insulated  wire  (you  will  need  about  8  feet  of  wire  for  a  bar  |  in. 
in  diameter). 

Hold  one  end  of  the  bar  near  iron  filings  and  pass  a  current 
through  the  wire.  Is  the  bar  a  magnet  ? 

Stop  the  current.     Is  the  bar  a  magnet? 

A  bar  of  soft  iron  wound  with  insulated  wire  in  this  way  is  an  elec- 
tromagnet, and  the  important  property  of  an  electromagnet  is  that 
it  is  a  magnet  only  when  the  current  is  flowing  through  the  wire. 

The  following  rule  enables  us  to  find  the  N  pole  of  an  electro- 
magnet when  we  know  the  direction  in  which  the  current  is  flowing. 

RULE  :  Grasp  the  electromagnet  in  the  right  hand  with  the  fingers 
pointing  in  the  direction  the  current  is  flowing  in  the  wire  ;  the  ex- 
tended thumb  then  points  to  the  north  pole  of  the  electromagnet. 

Test  this  rule  as  follows :  Place  the  electromagnet  on  the  table 
at  right  angles  to  a  compass  needle  and  about  2  in.  from  it.  Pass 
the  current  through  the  wire  first  in  one  direction  and  then  in  the 
other.  Does  the  rule  give  the  N  pole  of  the  electromagnet  in 
each  case? 

Wind  a  soft  iron  horseshoe  with  the  wire  to  make  a  horseshoe 
electromagnet.  Place  the  ends  near  iron  filings  and  pass  the 
current  through  the  wire.  Is  the  horseshoe  a  magnet? 

Stop  the  current.  Is  the  horseshoe  a  magnet?  Test  the  rule 
for  finding  the  N  pole. 

SOLENOID 

Make  a  solenoid  by  winding  a  dozen  turns  of  wire  on  a  lead 
pencil.  Remove  the  coil  from  the  pencil  and  place  it  on  the  table 


LABORATORY  COURSE  IN  PHYSICS  75 

near  a  compass  and  at  right  angles  to  the  needle.  Pass  the  current 
through  the  coil.  Is  the  coil  a  magnet  ? 

A  coil  of  wire  with  a  current  passing  through  it  is  called  a  sole- 
noid ;  it  is  a  magnet,  but  weaker  than  an  electromagnet  of  the 
same  size. 

Test  the  rule  for  finding  the  N  pole  of  an  electromagnet  on  the 
solenoid.  Does  it  enable  you  to  find  the  N  pole  of  the  solenoid 
when  you  know  the  direction  the  current  is  flowing  through  the 
wire? 


76  LABORATORY  COURSE  IN  PHYSICS 


LABORATORY  COURSE  IN  PHYSICS  77 

Experiment  25.     Applications  of  the  electromagnet. 

To  study  the  electric  bell  and  the  telegraph. 

Electric  bell.  Six  insulated  wires  i£  feet  long. 

Push  button.  Two  insulated  wires  8  feet  long. 

Two  dry  cells.  Two  telegraph  sounders. 

Two  keys. 

As  we  continue  our  study  of  electricity  we  shall  find  that  when 
it  is  necessary  to  move  anything  in  or  with  an  electrical  appliance, 
an  electromagnet  is  almost  always  used  to  produce  the  movement. 

THE  ELECTRIC  BELL 

Method.  Join  an  electric  bell  to  a  dry  cell  and  push  button  in 
such  a  way  that  the  bell  rings  when  the  button  is  pressed.  Do  you 
find  the  electromagnet? 

Trace  the  path  of  the  current  through  the  bell. 

Study  the  bell  to  find  out  why  it  continues  to  ring  as  long  as 
the  button  is  pressed.  Consult  the  text  book  if  necessary. 

Make  a  diagram  of  the  bell  in  your  note  book  showing  the  path 
of  the  current  through  the  bell. 


1 


THE  TELEGRAPH 

Join  a  sounder  to  a  dry  cell  and  key  in  such  a  way  that  the 
sounder  sounds  when  the  key  is  pressed.  Do  you  find  the  electro- 
magnet ? 

Follow  the  current  through  the  sounder  and  key. 

NOTE. — When  using  a  dry  cell  do  not  allow  the  current  to  run  for 
long  at  a  time. 

Let  two  groups  of  students  join  two  such  stations  by  two  line 
wires  in  such  a  way  that  each  station  has  a  sounder,  key,  and  cell, 
and  that  both  sounders  sound  when  either  key  is  pressed,  the  other 
key  being  closed. 

Make  a  diagram  in  your  note  book  of  two  telegraph  stations 
connected  by  two  line  wires,  each  station  being  equipped  with 
sounder,  key,  and  cell.  See  text  if  necessary. 


78  LABORATORY   COURSE   IN   PHYSICS 

Exercise  22.     Bell  Circuit. 

Examine  the  electric  doorbell  of  the  school.  Locate  the  push 
button,  battery  and  bell,  and  draw  on  paper  the  path  which  the 
wires  should  take  to  connect  these  properly.  Consult  page  178, 
Physics  of  the  Household. 

Now  follow  the  wires  to  determine  whether  they  are  as  you  have 
drawn  them. 

Unscrew  the  top  of  the  push  button  and  make  a  diagram  of 
the  interior.  Consult  page  179,  Physics  of  the  Household. 

Remove  the  box  of  the  bell  and  make  a  diagram  of  the  wiring. 
Consult  page  178,  Physics  of  the  Household. 

What  type  of  cell  is  used  in  the  battery?  Consult  pages  164- 
167,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  these  exercises  with  the  electric  bell  in  your  home  and 
make  a  written  report. 


LABORATORY  COURSE  IN  PHYSICS 


79 


Experiment  26.     Electric  motor. 
To  study  the  electric  motor. 


Fig.  3 

FIG.  31.  Diagrams  showing  the  demonstration  motor  arranged :  in  Fig.  i,  as  a  motor 
with  permanent  magnets  in  the  field  magnet;  in  Fig.  2,  as  a  shunt  wound  motor  with 
an  electromagnet  for  the  field  magnet;  in  Fig.  3,  as  a  series  wound  motor  with  an 
electromagnet  for  the  field  magnet. 


Demonstration  motor. 


Dry  cell. 


Compass. 


Method.  The  armature.  The  moving  part  of  the  motor  is 
called  the  armature;  the  split  ring  on  one  end  of  the  armature  is 
called  the  commutator;  and  the  magnets  or  magnet  are  called  the 
field  magnets  or  magnet. 

Connect  a  dry  cell  B  with  the  motor  as  shown  in  Fig.  i  above. 
Does  the  armature  revolve  ? 

Disconnect  one  wire,  place  the  armature  in  a  position  parallel 
to  the  magnets  and  move  the  permanent  magnets  back.  Follow 
path  of  the  current:  from  the  carbon  pole  of  the  cell  to  the 
)rush,  commutator  section,  around  the  armature,  to  the  second 

)mmutator  section,  to  the  second  brush  and  back  to  the  zinc 

>le  of  the  cell. 

Use  the  rule  for  finding  the  N  pole  of  an  electromagnet  to  find 


80  LABORATORY   COURSE   IN   PHYSICS 

the  N  pole  of  the  armature.  Check  this  by  testing  with  a  com- 
pass, with  the  current  flowing  through  the  armature. 

Now  move  the  N  pole  of  the  armature  through  \  turn  and  test 
it  again  with  the  compass.  Is  it  now  a  S  pole?  Why? 

Do  the  armature  poles  change  each  half  revolution?  That  is, 
is  each  end  of  the  armature  a  N  pole  in  one  half  turn  and  a  S  pole 
in  the  other  half  turn  ?  Where  are  the  ends  of  the  armature  when 
the  change  is  made? 

Connect  the  cell  and  notice  the  direction  in  which  the  armature 
revolves.  Reverse  the  direction  of  the  current.  Is  the  direction 
the  armature  revolves  reversed?  Why? 

The  field  magnet.  Connect  the  cell  and  notice  the  direction 
the  armature  revolves. 

Reverse  both  magnets.  Is  the  direction  the  armature  revolves 
reversed?  Why? 

Reverse  one  magnet  only,  to  make  the  ends  near  the  armature 
either  both  N  or  both  S.  Does  the  armature  revolve?  Why? 

Make  one  pole  near  the  armature  N  and  the  other  S.  Move 
each  pole  back  2  in.  and  connect  the  cell.  Does  the  armature 
revolve  as  rapidly  when  the  magnetic  field  is  weakened? 

Move  the  magnets  back  and  attach  the  electromagnet  (field 
magnet)  as  shown  in  Fig.  2  ;  connect  the  cell  and  notice  the  direc- 
tion the  armature  revolves. 

Use  the  rule  for  finding  the  N  pole  of  an  electromagnet  to  find 
the  N  pole  of  the  field  magnet.  Check  this  with  a  compass.  Do 
you  understand  from  this  why  the  armature  revolves  in  the  direc- 
tion it  does  ? 

Reverse  the  direction  of  the  current.  Is  the  direction  the  arma- 
ture revolves  reversed?  Why  not?  Is  it  because  the  current  is 
reversed  in  both  the  armature  and  the  field  magnet  ? 

Connect  the  cell  and  notice  the  direction  in  which  the  armature 
revolves.  Then  reverse  the  direction  of  the  current  in  the  field  mag- 
net only,  by  connecting  the  field  magnet  wires  to  the  opposite  bind- 
ing posts.  Is  the  direction  in  which  the  armature  revolves  reversed  ? 


LABORATORY   COURSE   IN   PHYSICS 


8l 


Follow  the  path  of  the  current  from  the  carbon  pole  of  the  cell 
to  the  first  binding  post  of  the  motor.  Do  you  notice  that  the 
current  divides  here  and  that  part  of  it  goes  through  the  armature 
and  part  through  the  field  magnet?  These  parts  unite  at  the 
second  binding  post  and  return  to  the  zinc  pole  of  the  cell.  When 
a  current  is  divided  in  this  way  each  part  is  called  a  shunt  of  the 
other.  A  motor  arranged  in  this  way  is  called  a  shunt  wound 
motor. 

Connect  the  field  magnet  as  shown  in  Fig.  3.  Follow  the  path 
of  the  current.  Do  you  notice  that  the  current  flows  through 
the  armature  and  field  magnet  one  after  the  other,  that  is,  in 
series?  A  motor  arranged  in  this  way  is  called  a  series  wound 
motor. 

Connect  the  cell  and  notice  the  direction  the  armature  revolves. 
Reverse  the  direction  of  the  current.  Is  the  direction  the  arma- 
ture revolves  reversed?  Why  not?  Is  it  because  the  current  is 
reversed  in  both  the  armature  and  the  field  magnet? 

Reverse  the  direction  of  the  current  through  the  field  magnet 
only,  as  follows  :  Disconnect  the  field  magnet  wire  from  the  bind- 
ing post  and  connect  the  other  field  magnet  wire  to  this  post. 
Connect  the  cell.  Is  the  direction  in  which  the  armature  revolves 
reversed  ?  Why  ? 

Exercise  23.     Electric  Motors. 

Examine  one  or  more  of  the  school  motors  and  identify  the 
field  magnet,  armature,  brushes,  and  commutator,  or  rings  if  the 
motors  run  on  alternating  current.  Consult  page  183,  Physics 
of  the  Household. 

Examine  the  name  plate  on  each  motor  and  learn  the  voltage 
for  which  it  is  made  and  the  amperage  of  the  current  it  uses. 

Calculate  the  power  of  the  current  in  watts  and  horse  power, 
remembering  that :  watts  =  volts  X  amperes,  and  that  746 
watts  =  i  horse  power.  Consult  pages  208-210,  Physics  of  the 
Household. 


82  LABORATORY  COURSE  IN  PHYSICS 

Calculate  the  number  of  40-watt  tungsten  lamps  which  could 
be  lighted  with  the  current  used  in  the  motor. 

Find  the  cost  of  the  city  current  per  kilowatt  hour  and  calculate 
the  cost  of  running  each  motor  for  one  hour. 

Home  Exercise. 

Repeat  this  exercise  with  the  electric  motor  in  your  home  and 
make  a  written  report. 

Exercise  24.     Electric  Heating  and  Cooking  Appliances. 

Examine  one  of  each  type  of  electric  heating  and  cooking  ap- 
pliances in  the  school  and  learn  as  much  as  you  can  about  how 
each  is  heated.  Consult  pages  187-191,  Physics  of  the  Household. 

Examine  the  name  plate  on  each  to  learn  the  voltage,  amperage, 
and  watts  of  the  current  used. 

NOTE.  —  In  some  cases  the  amperage  is  given  and  in  others  the  watts. 

Calculate  the  watts  of  the  current  used  in  each  appliance  (watts 
=  volts  X  amperes)  and  then  calculate  the  number  of  40-watt 
tungsten  lamps  which  could  be  lighted  with  the  current  used  in 
each. 

Find  the  cost  of  the  city  current  per  kilowatt-hour  and  calculate 
the  cost  of  running  each  appliance  for  i  hour  and  for  10  hours. 
Consult  page  209,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  this  exercise  with  the  electric  heating  and  cooking  ap- 
pliances in  your  home  and  make  a  written  report. 

Exercise  25.     Electric  Lighting. 

Trace  the  path  of  the  electric  light  wires  from  the  point  at  which 
they  enter  the  school,  to  the  switch-box  and,  if  possible,  some 
distance  along  each  branch. 

Make  a  diagram  of  this  part  of  the  lighting  circuit  and  show  on 
it  the  main  switch,  the  fuses,  the  meter,  the  main  wires,  and  the 
branch  wires.  Consult  page  215,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  this  exercise  with  the  electric  light  wires  in  your  home. 


LABORATORY   COURSE  IN  PHYSICS  83 

From  the  price  of  the  city  current  per  kilowatt-hour,  calculate 
the  cost  per  hour  of  the  current  used  in  one  electric  light  in  your 
home. 

Make  a  written  report  on  this  work. 

NOTE.  —  Carbon  lamps  of  16  candle  power  use  electric  current  at 
about  the  rate  of  55  watts;  tungsten  lamps  are  usually  marked  25  watts, 
40  watts,  60  watts,  etc.,  according  to  the  rate  at  which  they  use  current. 

Read  your  electric  current  meter  once  each  month  for  six  months, 
record  the  date  and  reading  and  compare  your  readings  with  those 
sent  in  by  the  electric  light  company. 


84  LABORATORY   COURSE   IN   PHYSICS 

Experiment  27.    Electrolysis,  Electroplating,  and  the  storage  cell. 

To  study  electrolysis  and  to  show  how  it  is  applied  in  electro- 
plating and  in  the  storage  cell. 

Two  tumblers.  Two  lead  strips. 

Dilute  H2SO4  (1-60).  Electric  bell. 

Concentrated  solution  of  CuS04.  Compass. 

One  copper  strip.  Two  dry  cells, 

One  carbon  rod.  Strip  holder. 

ELECTROLYSIS 

Method.  Attach  two  copper  wires  to  a  dry  cell  and  dip  the 
clean  bare  ends  in  dilute  sulphuric  acid.  Do  you  notice  that 
bubbles  of  gas  are  formed  on  one  end  but  none  at  all  on  the 
other  ?  Do  the  bubbles  appear  on  the  anode  (the  way  in)  or  on 
the  cathode  (the  way  out)  ? 

When  H2SO4  is  dissolved  in  water  it  breaks  up  into  positively 
charged  H  ions  and  negatively  charged  SO4  ions.  When  a  current 
is  passed  through  this  solution  the  H  ions  move  with  the  cur- 
rent and  are  liberated  at  the  cathode  (these  are  the  bubbles 
you  see) ;  the  SO4  ions  move  in  the  opposite  direction  and  are 
liberated  at  the  anode.  In  this  case  the  anode  is  copper  and  the 
SO4  ions  unite  with  it  to  form  CuSO4,  and  for  this  reason  no  bub- 
bles appear. 

Place  the  bare  ends  of  the  copper  wire  in  a  concentrated  solu- 
tion of  CuSO4.  Do  you  notice  bubbles  on  either  the  cathode  or 
the  anode?  After  the  current  has  run  for  one  minute  examine 
the  cathode  and  the  anode.  Which  has  received  a  bright  covering 
of  copper? 

When  CuSO4  is  dissolved  in  water  it  breaks  up  into  positively 
charged  Cu  ions  and  negatively  charged  SO4  ions.  When  a  current 
is  passed  through  this  solution  the  Cu  ions  move  with  the  current 
and  are  deposited  on  the  cathode  (this  is  the  bright  coating  of 
copper) ;  the  SO4  ions  move  in  the  opposite  direction  and  are 
deposited  on  the  anode  as  explained  above. 


LABORATORY  COURSE  IN  PHYSICS 


86  LABORATORY  COURSE  IN  PHYSICS 

ELECTROPLATING 

Place  a  copper  strip  and  a  carbon  rod  in  a  concentrated  solution 
of  CuSO4 ;  connect  the  copper  plate  with  the  carbon  pole  of  a  dry 
cell  and  the  carbon  rod  with  the  zinc  pole.  Allow  the  current  to 
run  for  two  minutes  and  examine  the  carbon  rod. 

NOTE.  —  In  these  experiments  you  must  allow  the  current  from  the 
dry  cells  to  run  for  two  and  three  minutes.  This  uses  up  the  cells  very 
rapidly  and  for  this  reason  and  others  it  will  be  necessary  to  purchase 
new  dry  cells  each  year. 

Is  the  carbon  rod  plated  with  copper  ? 

Reverse  the  current  and  allow  it  to  run  for  two  or  three  minutes. 
Is  the  copper  removed  from  the  carbon  rod  ? 

THE  STORAGE  CELL 

Place  two  lead  plates  (i  in.  by  4  in.)  in  dilute  sulphuric  acid  and 
connect  them  with  two  dry  cells  joined  in  series.  Allow  the  current 
to  run  for  three  minutes  and  then  disconnect  the  dry  cells  and 
connect  the  storage  cell  with  an  electric  bell.  Has  the  storage  cell 
been  charged?  Consult  your  text  book  and  answer  these  ques- 
tions : 

What  gases  appear  at  the  cathode  and  anode  ? 

What  substances  are  formed  on  the  cathode  and  anode  when 
the  storage  cell  is  charged  ? 

Direction  of  charging  and  discharging  currents.  Connect  the 
dry  cells  with  the  storage  cell  again  for  one  half  minute  and  with  a 
compass  find  the  direction  of  the  charging  current  (check  by  follow- 
ing the  wire  to  the  dry  cells).  Disconnect  the  dry  cells  and  find 
the  direction  of  the  discharging  currents  of  the  storage  cell  by 
means  of  the  compass. 

Do  the  charging  current  and  the  discharging  current  flow  in 
opposite  directions? 


LABORATORY  COURSE  IN   PHYSICS 


Experiment  28.     Measurement  of  resistance. 

To  learn  how  to  measure  resistance  by  means  of  a  Wheatstone 
bridge. 


FIG.  33.     Diagram  illustrating  the  principle  of  the  Wheatstone  bridge. 


Two  dry  cells. 

Key. 

Wheatstone  bridge. 


D'Arsonval  galvanometer. 

Resistance  box. 

One  yard  #  30  G.  S.  wire. 


The  principle  of  the  Wheatstone  bridge  is  illustrated  in  Fig.  33. 
There  are  four  resistances  R,  X,  m,  and  n.  The  current  from  the 
battery  flows  to  A  and  divides ;  one  part,  /i,  flows  through  the 
resistances  R  and  X,  and  the  other  part,  /2,  through  the  resistances 
m  and  n.  The  two  parts  unite  at  B  and  flow  back  to  the  battery. 
There  is  a  continual  fall  in  potential  from  A  to  B  along  both 
branches  of  the  circuit,  and  if  we  choose  some  point  C  in  the  branch 
A,  C,  B,  there  must  be  some  point  D  in  the  branch  A,  D,  B  which 
is  at  the  same  potential  as  C.  If  these  points  C  and  D  are  con- 
nected through  a  galvanometer  G,  there  is  no  current  through  the 
galvanometer,  because  C  and  D  are  at  the  same  potential.  When 
these  points  C  and  D  are  found,  the  ratio  of  the  resistance  X  to 
the  resistance  R  is  the  same  as  the  ratio  of  the  resistance  n  to 
the  resistance  m,  or 

X      n          (i) 

R      m 

If  then  R,  m  and  n  are  known  resistances,  the  resistance  of  X 
can  be  calculated. 

The  apparatus  you  will  use  is  illustrated  in  Fig.  34.     Two  dry 


88  LABORATORY   COURSE   IN  PHYSICS 

cells  are  connected  through  a  key  K  to  the  points  A  and  B.  R  is 
a  known  resistance  (a  resistance  box  or  a  coil  of  known  resistance), 
X  is  the  unknown  resistance.  mDn  is  a  piece  of  #30  German-sil- 
ver wire  i  meter  long  stretched 
over  a  meter  stick.  G  is  a 
D'Arsonval  galvanometer  with 
one  terminal  connected  at  C 
and  with  the  other  terminal  D 

FIG.  34-    Diagram  of  the  slide  wire  bridge    fre£   t()  ^^  ^  ^  wire  ^ 

used  to  measure  the  resistance  of  wire. 

The  resistances  of  m  and  n  are 
proportional  to  their  lengths,  which  are  read  on  the  meter  stick. 

The  current  from  the  dry  cells  enters  at  A  and  divides.  Part 
of  it  flows  through  R  and  X  and  part  of  it  through  m  and  n. 
When  a  point  D  is  found  such  that  there  is  no  current  through  the 
galvanometer  we  can  calculate  X  by  inserting  R,  m,  and  n  in  (i). 

Method.  Insert  i  yard  of  #30  German-silver  wire  at  X  and  a 
resistance  box  at  R.  Place  the  sliding  point  D  at  the  50  cm.  mark. 
Remove  the  i  ohm  plug  from  the  resistance  box  R,  close  the  key  and 
observe  the  direction  the  galvanometer  needle  turns.  Repeat 
with  the  10  ohm  plug  removed,  and  if  the  galvanometer  needle 
turns  in  the  opposite  direction  you  know  the  resistance  is  between 
i  and  10  ohms.  Try  plugs  between  i  and  10  until  the  deflection 
is  small  and  then  obtain  the  point  of  no  deflection  by  moving  D 
back  and  forth.  When  this  point  is  found  measure  m  and  n 
and  the  resistance  R.  Insert  these  values  in  (i)  and  calculate  X. 

Measure  the  resistance  of  i  yard  of  #30  iron  wire  in  the  same 
way. 

FORM    OF   REPORT 


GERMAN  SILVER 

IRON 

Length  of  m          

Length  of  n           

Resistance  X 

LABORATORY  COURSE  IN  PHYSICS  89 

Experiment  29.     Resistance   measured  by  voltmeter-ammeter 
method. 

To  find  the  resistance  of  a  number  of  appliances  by  the  volt- 
meter-ammeter method. 

To  find  the  electrical  power  used  in  each  appliance. 
To  find  the  eificiency  of  a  water  heating  appliance. 


Power 
Current. 


Voltmeter 


FIG.  35.  Diagram  showing  how  to  arrange  the  apparatus  to  measure  the  resistance 
of  electric  appliances  and  the  electrical  power  used  in  them. 

Voltmeter.  Balance  (gram). 

Ammeter.  Vessel. 

Electric  iron,  stove,  water  heater,  etc.         Thermometer. 

Method.  Resistance.  Connect  the  electric  iron  with  the  am- 
meter, voltmeter,  and  power  circuit  as  shown  in  Fig.  35.  Read 
the  E.M.F.  in  volts  and  the  current  in  amperes.  Use  Ohm's 
law  (amperes  =  volts  -5-  ohms)  to  calculate  the  resistance  of  the 
iron  in  ohms.  Repeat  with  the  stove. 


9° 


LABORATORY   COURSE   IN   PHYSICS 


Power.  The  electrical  power  used  in  any  appliance  in  watts 
is  found  by  multiplying  the  current  in  amperes  by  the  E.M.F. 
in  volts,  that  is,  watts  =  amperes  X  volts. 

Use  the  results  obtained  above  to  calculate  the  electrical  power 
used  in  each  appliance. 

The  efficiency  of  a  water  heater.  Weigh  a  vessel  of  about  i 
liter  capacity.  Multiply  this  weight  by  the  specific  heat  of  the 
metal  of  which  the  vessel  is  made  (.095  for  copper,  .n  for  iron) 
to  find  the  number  of  calories  of  heat  required  to  warm  the  vessel 
i°  C. ;  this  is  called  the  water  equivalent  of  the  vessel. 

Add  500  g.  of  ice  water,  insert  the  water  heater  and  stir  with 
the  thermometer  continuously,  observe  and  record  the  exact  time 
when  the  water  is  15°  C.  below  room  temperature ;  also  record  the 
exact  time  when  it  is  15°  C.  above  room  temperature.  Record 
the  volts  and  amperes  at  the  low  temperature  and  at  the  high 
temperature. 

From  the  average  voltmeter  and  ammeter  readings  calculate 
the  power  in  watts. 

Now,  by  Joule's  law,  the  heat  in  calories,  produced  by  a  current 
=  watts  X  .24  X  seconds.  Calculate  the  heat  in  calories  given 
by  the  current  to  the  water  heater,  =  input. 

The  heat  in  calories  which  the  water  received  =  (weight  of  water 
+  water  equivalent)  X  change  in  temperature.  Calculate  the 
number  of  calories  received  by  the  water,  =  output. 

output      calories  received  by  water 

Efficiency  =  - — ^-7   =  — : — : : r~  — 

input         calories  given  by  current. 

Calculate  the  efficiency  of  the  water  heater. 
FORM    OF   REPORT 


VOLTS 

AMPERES 

RESISTANCE 

WATTS 

LABORATORY  COURSE  IN  PHYSICS 


VOLTS 

AMPERES 

TIME 

Water  heater,  beginning  . 
Water  heater,  end  .     .     . 

. 

Average  

Difference 

Weight  of  calorimeter  =  . 

Water  equivalent  of  calorimeter  =  . 

Weight  of  water  =  . 

Water  +  water  equivalent  =  . 

Change  of  temperature  =  . 

Calories  produced  by  current  = 
Calories  received  by  water 

Efficiency  = 


LABORATORY   COURSE   IN   PHYSICS 


Experiment  30.     Cells  connected  in  series  and  in  parallel. 

To  find  the  electromotive  force  in  volts  of  cells  connected  in 
series  and  in  parallel. 

Five  dry  cells.  Voltmeter. 

Method.  Connect  one  dry  cell  with  a  voltmeter.  What  is  the 
E.M.F.  in  volts? 

Cells  in  series.  Connect  two  cells  in  series  and  connect  them 
with  the  voltmeter.  What  is  the  E.M.F.  of  two  cells  in  series? 

In  the  same  way  find  the  E.M.F.  of  3,  4,  5,  etc.,  dry  cells  joined 
in  series. 

Cells  in  parallel.  Connect  two  cells  in  parallel  and  connect 
them  with  the  voltmeter.  What  is  the  E.M.F.  of  two  cells  in 
parallel  ? 

In  the  same  way  find  the  E.M  F.  of  3,  4,  5,  etc.,  cells  in  parallel. 

Is  the  E.M.F.  of  n  cells,  in  series,  equal  to  n  times  the  E.M.F.  of 
one  cell? 

Is  the  E.M.F.  of  n  cells  in  parallel  equal  to  the  E.M.F.  of  one 
cell? 

FORM    OF   REPORT 


IN  SERIES 

IN  PARALLEL 

I^.M.F.  of  i  dry  cell  

volts 

volts 

E  M  F  of  2  dry  cells 

volts 

volts 

E.M.F.  of  3  dry  cells  
E.M.F.  of  4  dry  cells  
E.M.F.  of  5  dry  cells  .  .  . 

volts 
volts 
volts 

volts 
volts 
volts 

LABORATORY  COURSE  IN  PHYSICS 


93 


Experiment  31.     Induced  currents. 

To  study  induced  currents. 


n  n 


1'iG.  36.     Apparatus  used  to  illustrate  induced  currents. 


Coil. 

D'Arsonval  galvanometer. 

Two  magnets. 


Dry  cell. 
Electromagnet. 


Make  a  coil  about  2  in.  in  diameter  by  winding  about  1 5  feet  of 
$22  insulated  wire  about  two  fingers  held  apart,  and  connect  it 
with  a  delicate  galvanometer. 

Push  the  north  pole  of  a  permanent  magnet  into  the  coil.  Is  a 
current  produced? 

Allow  the  magnet  to  remain  in  the  coil.  Does  the  current  con- 
tinue ? 

Pull  the  north  pole  out  of  the  coil.  Is  there  a  current  produced? 
In  what  direction? 

Strength  of  E.M.F.  produced  in  the  coil.     Push  a  magnet  pole 


94  LABORATORY   COURSE  IN  PHYSICS 

into  the  coil  slowly  and  then  rapidly.  Which  produces  the  greater 
effect? 

Hold  together  the  like  poles  of  two  magnets  and  push  them  into 
the  coil.  Is  the  effect  greater  than  that  produced  by  one  magnet 
pole? 

Direction  of  E.M.F  produced  in  coil.  Lent's  Law  states  that 
the  direction  of  the  current  produced  by  induction  is  always  such 
that  its  magnetic  field  opposes  the  motion  of  the  thing  producing  it. 

Test  this  as  follows.  In  order  to  know  the  direction  of  the  in- 
duced current  in  the  coil,  we  must  know  how  the  galvanometer 
needle  turns  when  the  current  enters  the  galvanometer  through 
one  binding  post  or  the  other.  To  find  this,  connect  the  galva- 
nometer with  a  dry  cell  (through  a  high  resistance,  to  avoid  damag- 
ing the  galvanometer),  and  notice  the  direction  the  needle  moves. 
We  know  the  current  from  the  dry  cell  comes  from  the  carbon  pole. 
By  noticing  the  binding  post  through  which  the  current  from  the 
dry  cell  enters  the  galvanometer,  and  the  direction  the  needle 
moves,  we  can  afterwards  tell  the  direction  of  any  current  which 
enters  the  galvanometer. 

Connect  the  coil  with  the  galvanometer.  Push  the  north  pole 
of  the  magnet  into  the  coil.  Is  the  current  produced  in  the  coil 
in  such  a  direction  as  to  make  the  top  of  the  coil  a  north  pole 
(rule,  page  74)  and  thus  to  oppose  the  downward  motion  of  the 
north  pole  of  the  magnet  ? 

Pull  the  north  pole  of  the  magnet  out  of  the  coil.  Is  the  direc- 
tion of  the  induced  current  in  the  coil  such  as  to  make  the  top  of 
the  coil  a  south  pole,  and  thus  to  oppose  the  upward  motion  of 
the  north  pole  of  the  magnet  ? 

Test  the  direction  of  the  currents  produced  by  the  south  pole 
in  the  same  way. 

Induced  currents  produced  by  an  electromagnet.  Find  the 
north  pole  of  an  electromagnet  (rule,  page  74)  and  push  it  into 
the  coil.  Does  it  act  in  the  same  way  as  a  permanent  magnet  ? 

Place  the  electromagnet  in  the  coil,  and  then  start  and  stop  the 


LABORATORY  COURSE  IN  PHYSICS  95 

current  in  the  electromagnet.  Is  the  effect  the  same  as  though 
the  electromagnet  were  moved  into  and  out  of  the  coil?  Is  the 
direction  of  the  induced  current  in  the  coil  opposite  to  that  in  the 
electromagnet  when  the  current  is  starting  in  the  electromagnet, 
and  in  the  same  direction  when  the  current  in  the  electromagnet 
is  stopping?  Is  an  induced  current  produced  in  the  coil  when 
the  current  in  the  electromagnet  is  neither  starting  nor  stopping, 
but  is  running  steadily  ? 

FORM    OF   REPORT 

How  is  an  induced  current  produced  ? 

Is  the  effect  greater  or  less  when  the  magnet  is  moved  quickly? 
Is  the  effect  greater  when  two  magnets  are  used  ? 

Make  diagrams  in  your  note  book  showing  the  direction  of  the  in- 
duced current  produced  in  the  coil  by  the  magnet.  Make  two  diagrams 
for  the  N  pole  and  two  for  the  S  pole. 


96  LABORATORY  COURSE  IN  PHYSICS 

Experiment  32.     Applications  of  induced  currents. 
To  study  the  magneto,  dynamo,  and  induction  coil. 

Magneto.  Induction  coil. 

Dynamo.  Two  dry  cells. 

Motor.  Galvanometer. 

Incandescent  lamp.  Four  spikes  for  handles. 
Iron  wire  $30. 

Let  the  class  be  divided  into  three  groups  and  let  each  group 
work  one  third  of  the  period  with  each  appliance. 

MAGNETO 

Method.  Connect  two  metal  handles  to  the  magneto  binding 
posts  by  means  of  wires  and  let  each  student  in  turn  hold  the 
handles  while  another  operates  the  magneto.  Can  the  current  be 
felt? 

In  order  that  a  current  may  be  felt  it  is  necessary  that  the 
electromotive  force,  in  volts,  of  the  current  be  high.  In  the 
text  book  we  learn  that  the  electromotive  force  of  an  induced 
current  depends  upon:  the  strength  of  the  magnetic  field,  the 
number  of  turns  of  wire  on  the  coil,  and  the  speed  with  which  the 
magnetic  lines  of  force  are  cut. 

Remove  the  magnets  and  examine  the  interior.  Is  the  electro- 
motive force  of  the  induced  current  high  for  the  following  reasons : 

(1)  a  strong  magnetic  field  is  produced  by  four  or  five  strong 
magnets ; 

(2)  there  are  many  turns  of  wire  on  the  revolving  coil  (the 
armature) ; 

(3)  the  coil  is  so  geared  that  it  can  be  revolved  rapidly. 

Turn  the  coil  without  the  magnets.  Can  a  current  be  felt? 
Why?  Replace  the  magnets  and  connect  the  magneto  with  the 
2  5- turn  coil  of  a  galvanometer.  Turn  the  handle  slowly  and 
observe  whether  the  current  is  direct  or  alternating. 


LABORATORY   COURSE   IN   PHYSICS 


97 


98  LABORATORY  COURSE  IN  PHYSICS 

DYNAMO 

Connect  a  hand  power  dynamo  with  an  incandescent  lamp  of  suit- 
able voltage  and  amperage.  Turn  the  handle  and  light  the  lamp. 

In  this  case  the  mechanical  energy  supplied  by  your  arm  is 
transformed  into  electrical  energy  in  the  dynamo  and  this  in  turn 
is  transformed  into  light  and  heat  energy  in  the  lamp. 

While  one  student  is  operating  the  dynamo  let  another  turn 
the  lamp  on  and  off.  Is  more  energy  required  to  drive  the  dynamo 
when  the  light  is  on  than  when  it  is  off?  Why? 

Disconnect  the  lamp  and  join  the  two  wires  from  the  dynamo 
by  means  of  apiece  of  #30  iron  wire  about  i  in.  long.  Operate  the 
dynamo  and  heat  the  wire.  What  are  the  energy  transformations  ? 

If  a  second  similar  dynamo  is  available,  connect  them  and  turn 
the  handle  of  the  first  dynamo.  Does  the  armature  of  the  second 
dynamo  revolve?  Turn  the  handle  of  the  second  dynamo.  Does 
the  armature  of  the  first  dynamo  revolve?  What  does  this  illus- 
trate about  the  construction  of  a  dynamo  and  a  motor  ? 

Connect  the  dynamo  with  one  or  more  small  motors  and  oper- 
ate the  dynamo.  What  are  the  energy  transformations? 

Examine  the  dynamo.  Identify  the  field  magnet,  armature, 
commutator,  and  brushes.  Is  the  dynamo  shunt  wound  or  series 
wound? 

INDUCTION  COIL 

Attach  two  metal  handles  to  the  terminals  of  the  secondary  coil  of 
a  small  demonstration  induction  coil.  Attach  one  or  two  dry  cells 
to  the  primary  coil  and  start  the  interrupter.  Let  each  student  in 
turn  hold  the  handles  while  another  pulls  out  the  brass  reducing 
tube  slowly.  Can  the  current  induced  in  the  secondary  be  felt  ? 

Take  the  induction  coil  apart,  and  identify  the  primary  coil, 
secondary  coil,  soft  iron  core,  and  interrupter.  Follow  the  path 
of  the  current  from  the  battery  through  the  interpreter  and  the 
primary  coil. 

NOTE.  —  These  small  coils  usually  lack  a  condenser. 


LABORATORY  COURSE  IN  PHYSICS  99 

Exercise  26.     Electric  Light  Plant. 

As  a  class  visit  an  electric  light  plant  or  an  electric  power  plant, 
e.g.  street-car  power  plant.  Locate  the  dynamo  and  the  source 
of  power,  that  is,  boiler  and  engine  or  water  wheel. 

On  the  dynamo  identify  the  field  magnet,  armature,  brushes, 
and  commutator  or  rings. 

On  the  switchboard  identify  the  voltmeter,  ammeter,  and 
kilowatt  meter. 

Make  a  rough  diagram  showing  the  location  of  the  source  of 
power,  the  dynamo,  the  switchboard,  and  of  the  wires  to  and  from 
the  switchboard. 

Home  Exercise. 

Examine  the  lighting  plant  on  an  electrically  lighted  automobile. 
Locate  the  dynamo,  the  storage  battery,  the  lights,  and  the  wires 
connecting  these. 

Make  a  rough  diagram  of  the  plant  and  make  a  written  report. 

Exercise  27.     Telephone  Exchange. 

As  a  class  visit  the  telephone  exchange  in  your  town  or  city  and 
have  the  officer  in  charge  explain  to  you  what  happens  when  you 
ring  up  central  and  ask  for  any  number. 

Home  Exercise. 

In  your  own  home  follow  the  telephone  wires  from  the  point  at 
which  they  enter  your  house  to  the  telephone. 

Open  your  telephone  and  examine  the  interior ;  follow  the  wire 
from  the  battery  (if  it  is  a  battery  telephone)  to  the  transmitter, 
the  induction  coil,  and  back  to  the  battery :  follow  one  line  wire  to 
the  induction  coil,  the  receiver,  and  back  to  the  other  line  wire. 

Exercise  28.     Wireless  Station. 

As  a  class  visit  the  wireless  station  in  your  city,  if  there  is  one, 
and  ask  the  operator  to  explain  how  the  spark  is  produced,  how  a 
message  is  sent,  and  how  one  is  received. 


100 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  33.     Horse-power  and  efficiency  of  an  electric  motor. 

To  determine  the  horse-power  and  efficiency  of  an  electric  motor 
by  means  of  a  Prony  brake. 


1 


LABORATORY  COURSE  l?v j P&YS1C&  '*"  :  '' '*  '      :  IOI 


Motor  for  no  or  220  volt  current. 

Voltmeter. 

Two  spring  balances. 

Ammeter  (0-5  amperes). 


Watch. 

Cord  or  belt. 

Speed  counter. 

Support  and  large  clamp. 


Method.  Arrange  the  circuit  as  shown  in  Fig.  39 ;  the  current 
flows  through  the  motor  M  and  ammeter  A  in  series  and  through 
the  voltmeter  V  and  motor  in  parallel.  The  Prony  brake  B  con- 
sists of  two  spring  balances  with  a  cord  or  belt  attached  to  the  hooks. 
Place  the  cord  under  the  pulley  of  the  motor  and  raise  the  balances 
until  each  records  about  2  Ib. 

Horse-power.  To  determine  the  horse-power  of  the  motor  we 
must  measure: 

(1)  The  number  of  revolutions  per  second. 

(2)  The  circumference  of  the  pulley  expressed  in  feet. 

(3)  The  difference  in  the  readings  of  the  brake  balances,  ex- 
pressed in  pounds,  when  the  motor  is  running. 

It  will  be  remembered  that  one  horse  power  is  the  power  to  do 
33000  foot  pounds  of 
work  per  minute,  or 
33000  -r-  60  =  550 
foot  pounds  of  work 
per  second.  You 
will  find  the  number 
of  foot  pounds  of 
work  the  motor  does 
per  second  and  di- 
vide this  number  by 
550  to  find  the  horse- 
power of  the  motor. 

To  find  the  number 
of    revolutions    per 
second,    adjust    the 
brake,  then  let  one  student  hold  the  speed  counter  against  the  end 
of  the  pulley  and  give  to  another  student  the  signal  when  to  start 


FIG.  39.    Diagram  showing  how  to  arrange  the  apparatus. 


3    r»  s     -»  xc.a  .-.      *>°» 

. 

102  LAiiOliATORV   COURSE   IN  PHYSICS 

keeping  time  and  also  announce  i,  2,  3,  etc.,  to  10,  at  the  end  of 
each  100  revolutions.  In  this  way  find  the  number  of  seconds 
required  to  make  1000  revolutions  and  from  this  calculate  the 
number  of  revolutions  per  second. 

To  find  the  brake  load  in  pounds,  read  each  balance  in  ounces 
when  the  motor  is  running  and  divide  the  difference  by  16. 

To  find  the  circumference  of  the  pulley  in  feet,  pass  a  cord  arou"  1 
the  pulley  four  times  ;  measure  the  length  of  the  cord  in  inchc  "  , 
divide  the  result  by  four  and  then  by  twelve. 

Calculate  the  horse-power  of  the  motor  as  follows  :  The  braks 
load  in  pounds  multiplied  by  the  circumference  of  the  pulley  in  feet 
gives  the  foot  pounds  of  work  done  by  the  motor  in  one  revolution. 
This  multiplied  by  the  number  of  revolutions  per  second  gives  the 
foot  pounds  of  work  done  by  the  motor  in  one  second.  This 
number  divided  by  550  gives  the  horse-power  of  the  motor. 

TT  p    _  Load  in  Ib.  X  circ.  in  ft.  X  revolutions  per  second, 

550 

Efficiency.  The  efficiency  of  any  machine  is  equal  to  the  output 
divided  by  the  input.  You  have  just  found  the  output  in  horse- 
power. You  must  now  find  the  input  in  horse-power.  It  will  be 
remembered  that  a  rate  of  working  of  746  watts  =  i  horse-power. 
To  find  the  input,  then,  read  the  fall  in  potential  in  the  motor  in 
volts  and  the  number  of  amperes  used  by  the  motor.  The  product 
of  these  equals  the  watts,  or  the  rate  at  which  electric  energy  is 
supplied  to  the  motor.  This  number  divided  by  746  gives  the 
horse-power  supplied. 

H  P    ~  volts  X  amperes  =  input. 
746 

Efficiency  = 


input 

Make  the  load  greater  and  determine  again  the  output,  input, 
and  efficiency.  Is  the  efficiency  greater  or  less  on  the  heavier 
load? 


LABORATORY   COURSE  IN   PHYSICS 
FORM    OF   REPORT 


I03 


Revolutions  per  second       

Brake  load,  Ib  

Circumference  of  pulley,  feet  

Horse-power  output 

Fall  in  potential,  volts  

Current  amperes       

Horse-power  input 

Efficiency     

104 


LABORATORY   COURSE   IN   PHYSICS 


LIGHT 
Experiment  34.     The  photometer. 

To  determine  the  candle  power  of  an  oil  lamp,  a  16  candle  powei 
incandescent  carbon  lamp,  and  a  40  watt  tungsten  lamp. 


FIG.  40.     Illustrating  the  photometer. 


Bunsen  photometer  in  dark  room 

or  in  light-proof  box. 
Ordinary  oil  lamp. 


Carbon  lamp,  16  cp. 
Tungsten  lamp,  40  watt. 
Candle. 


The  candle  power  of  a  lamp  is  the  ratio  of  the  amount  of  light  given 
by  the  lamp  to  the  amount  given  by  a  standard  candle,  that  is,  it  is 
the  number  of  times  the  light  given  by  the  lamp  is  greater  or  less 
than  that  given  by  a  standard  candle. 

In  this  experiment  you  will  learn  simply  the  method  of  finding 
the  candle  power  of  a  lamp.  Your  results  will  not  be  exact  unless 
you  use  a  standard  candle  or  a  standard  lamp. 

Method.  Oil  lamp.  Arrange  the  Bunsen  photometer  as  shown 
in  Fig.  40.  Place  the  candle  B  at  one  end  of  the  photometer  and 
an  ordinary  oil  lamp  at  the  other;  then  move  the  grease  spot 
screen  A  back  and  forth  until  the  central  spot  and  the  surrounding 


LABORATORY   COURSE  IN  PHYSICS 


105 


paper  are  equally  illuminated.  When  this  point  is  found  we  know 
that  the  screen  is  receiving  the  same  amount  of  light  on  one  side, 
from  the  lamp,  that  it  is  on  the  other  side,  from  the  candle. 

Since  the  intensity  of  the  light  from  any  source  varies  inversely 
as  the  square  of  the  distance  between  the  source  and  the  object 
illuminated,  we  can  say: 

candle  power  of  lamp     _  (distance  from  lamp  to  screen)2 
candle  power  of  candle      (distance  from  candle  to  screen)2 

Measure  the  distance  from  the  lamp  to  the  screen  and  from  the 
candle  to  the  screen,  then  assume  that  the  candle  power  of  the 
candle  is  i  and  calculate  the  candle  power  of  the  lamp. 

Carbon  and  tungsten  lamps.  In  the  same  way  find  the  candle 
power  of  the  carbon  lamp  and  of  the  40  watt  tungsten  lamp. 

Assuming  that  the  16  candle  power  carbon  lamp  uses  55  watts 
and  the  tungsten  lamp  40  watts,  calculate  the  watts  required  per 
candle  power  for  each. 

Which  light  is  the  more  economical? 


FORM    OF    REPORT 


On.  LAMP 

CARBON  LAMP 

TUNGSTEN 
LAMP 

Lamp  to  screen 

cm. 

cm. 

cm. 

Candle  to  screen                 .     »     . 

cm. 

cm. 

cm. 

Candle  power       

The  carbon  lamp  requires 
The  tungsten  lamp  requires 


watts  per  candle  power 
watts  per  candle  power 


Exercise  29.     Lighting. 

Make  a  rough  diagram  of  one  class  room  in  your  school  showing 
how  the  light  is  admitted. 


106  LABORATORY   COURSE   IN  PHYSICS 

NOTE.  —  The  light  should  be  admitted  from  the  left  and  rear  of  a 
student  seated  at  his  desk ;  it  should  not  be  admitted  from  the  front, 
because  then  it  will  shine  directly  into  the  student's  eyes. 

Make  a  rough  diagram  of  your  school  kitchen  showing  where 
you  would  hang  the  electric  lamps  with  relation  to  the  table,  range, 
and  sink,  to  light  the  kitchen  properly  at  night.  Consult  page  247, 
Physics  of  the  Household. 

Home  Exercise. 

Make  a  diagram  of  your  home  kitchen  showing  where  you  would 
place  the  lights  if  you  were  consulted. 

Make  a  diagram  of  your  living  room  showing  how  you  would  place 
the  lamps  for  convenience  in  reading. 

Make  a  written  report. 


LABORATORY   COURSE  IN  PHYSICS 


107 


Experiment  35.     Reflection  of  light. 

To  show  that  the  angle  of  reflection  is  equal  to  the  angle  of 
incidence  and  that  an  object  and  its  image  are  equally  distant 
from  the  mirror. 


FIG    41      Apparatus  used  to  illustrate  the  reflection  of  light. 


Thin  mirror. 
Plain  glass  plate. 
Pins. 
Protractor. 


Paper. 
Ruler. 
Two  candles. 


108  LABORATORY   COURSE   IN   PHYSICS 

The  angle  of  reflection  equals  the  angle  of  incidence.  Method. 
Draw  a  line  on  a  piece  of  paper  and  mark  it  "mirror  line." 
Stand  a  thin  mirror  on  this  line,  perpendicular  to  the  paper. 

Stick  two  pins  upright  in  front  of  the  mirror  in  a  line  at  an  angle 
of  about  45°  to  the  mirror  line.  Number  these  pins  i  and  2.  Now 
set  up  two  pins  in  front  of  the  mirror  and  exactly  in  line  with  the 
images  of  pins  i  and  2.  Mark  these  pins  3  and  4.  Remove  the 
mirror  and  pins  and  draw  a  line  through  the  pin  holes  i  and  2  to 
the  mirror  line  and  a  line  through  the  pin  holes  3  and  4  to  the 
mirror  line.  These  lines  should  meet  at  the  mirror  line. 

At  the  point  of  intersection  of  the  lines  draw  a  line  perpendicular 
to  the  mirror  line.  Measure  the  angle  between  the  line  i  2  (the 
line  of  incidence)  and  the  perpendicular,  and  the  angle  between 
the  line  3  4  (the  line  of  reflection)  and  the  perpendicular.  Is 
the  angle  of  reflection  equal  to  the  angle  of  incidence? 

Repeat  this  with  a  different  angle  of  incidence. 

Distance  of  image  and  object.  Method  i.  Draw  a  line  on  a 
piece  of  paper  and  mark  it  "  mirror  line."  Place  the  mirror  on 
this  line  perpendicular  to  the  paper.  Place  a  pin  in  front  of  the 
mirror  and  about  15  cm.  from  it.  With  a  ruler  aim  at  the  image 
of  this  pin  from  two  positions  on  each  side  of  the  pin  and  draw 
lines  to  show  the  positions  of  the  ruler. 

Remove  the  mirror  and  continue  the  lines  solid  to  the  mirror 
line  and  as  dotted  lines  beyond  it.  The  place  at  which  the  dotted 
lines  meet  is  the  position  of  the  image.  Measure  the  perpendicular 
distance  of  image  and  object  from  the  mirror  line.  Are  they 
equal  ? 

Method  2.  Draw  a  line  on  a  piece  of  paper  and  place  a  piece 
of  plain  window  glass  on  the  line  perpendicular  to  the  paper.  Use 
two  candles  of  about  the  same  size.  Light  one  and  place  it  in 
front  of  the  glass,  then  place  the  unlighted  one  behind  the  glass 
in  such  a  position  that  the  unlighted  candle  and  the  image  of  the 
lighted  candle  coincide  when  viewed  from  any  point  in  front  of 
the  glass. 


LABORATORY   COURSE   IN   PHYSICS 


109 


The  unlighted  candle  then  gives  the  position  of  the  image  of  the 
lighted  candle.  Measure  the  distance  of  each  candle  from  the 
mirror  line.  Are  they  equal? 


FORM    OF   REPORT 


1ST   EXP. 

2D   EXP. 

Angle  of  reflection          .     .               .     .     .     . 

Angle  of  incidence     

PIN 

CANDLES 

Distance  of  image  from  mirror    .     .... 
Distance  of  object  from  mirror    .     .     . 

no 


LABORATORY  COURSE  IN  PHYSICS 


Experiment  36.     Index  of  refraction  of  glass. 
To  find  the  index  of  refraction  of  glass. 


FIG.  42.     Diagram  of  the  apparatus  used  to  measure  the  index  of  refraction  of  glass, 

Plate  glass  with  parallel  edges.  Paper. 

Ruler.  Pins. 

Compass. 

The  index  of  refraction  of  glass  is  the  ratio  of  the  speed  of  light  in 
air  to  its  speed  in  glass.  You  cannot  measure  the  speed  of  light 
in  air  or  glass  with  the  apparatus  at  hand,  but  the  index  of  refrac- 
tion of  glass  is  also  the  ratio  of  the  sine  of  the  angle  of  incidence  in 
air  to  the  sine  of  the  angle  of  refraction  in  glass,  and  these  you  can 
measure. 

•Method.  Draw  a  line  on  a  piece  of  paper  and  mark  it  "  plate 
line  "  ;  place  the  plate  glass  flat  on  the  paper  with  one  edge  exactly 
along  this  line.  Place  one  pin  at  some  point  A,  Fig.  42,  and 
another  at  a  point  B.  With  a  ruler  sight  through  the  glass  fronv 
B  to  the  image  of  A  and  draw  a  line  C  on  the  paper  along  the  edge 
of  the  ruler. 

Remove  the  glass  plate  and  draw  a  line  BA,  and  a  line  MEN 
perpendicular  as  to  the  plate  line  from  the  point  B.  Draw  a  circle 
with  B  as  center  and  draw  the  lines  GK  and  FH  perpendicular  to 
MEN. 

You  must  remember  that  you  see  the  image  of  the  pin  A  in  the 
glass  because  light  starting  from  A  passes  through  the  glass  to  B 
and  then  through  the  air  to  your  eye  at  G.  You  notice  that  the 


LABORATORY  COURSE  IN  PHYSICS  III 

image  of  A  in  the  glass  is  in  a  new  position.  The  reason  for 
this  is  that  the  light  which  travels  from  A  through  the  glass 
to  B  is  bent  away  from  the  perpendicular  MEN  when  it  enters 
the  air  at  B,  The  light  when  in  glass  makes  an  angle  b  with 
the  perpendicular  MBN  and  when  in  air  makes  the  larger  angle 
a.  To  prevent  confusion,  the  angle  a  in  air  is  always  called  the 
angle  of  incidence,  and  the  angle  b  in  the  other  medium  (in  this  case 
glass)  is  always  called  the  angle  of  refraction.  The  index  of  re- 
fraction of  glass  is  sine  a  -f-  sine  b.  Sine  a  is  GK/GB  and  sine 

b  is  FH/FB,  but  since  GB  =  FB  (radii  of  the  same  circle)  ^^  = 

sine  b 
f*v 

- —  =  index  of  refraction. 

Measure  GK  and  FH  carefully  and  calculate  the  index  of  re- 
fraction of  glass. 

The  index  of  refraction  of  glass  is  also,  as  stated  above,  the  ratio 
of  the  velocity  of  light  in  air  to  its  velocity  in  glass. 

FORM    OF   REPORT 

Length  of  GK  =          cm. 
Length  of  FH  =          cm. 
Index  of  refraction  of  glass  = 


112 


LABORATORY   COURSE   IN   PHYSICS 


Experiment  37.    Focal  length  and  conjugate  foci  of  a  converging 
lens. 

To  find  the  principal  focal  length  and  a  number  of  conjugate 
foci  of  a  converging  lens. 


FIG.  43.     Apparatus  us^d  to  measure  the  principal  focal  length  of  a  converging  lens 
and  to  find  pairs  of  congugate  foci  of  the  lens. 


Meter  stick  and  supports. 
Wire  netting  screen. 
White  cardboard  screen. 


Candle  or  lamp. 

Holders. 

Lens  about  15  cm.  focal  length. 


PRINCIPAL  FOCAL  LENGTH 

The  principal  focus  of  a  lens  is  the  point  at  which  rays  parallel 
to  the  principal  axis  of  the  lens  converge.  When  an  object  is  50  feet 
or  more  from  a  small  lens  the  rays  from  the  object  which  fall  upon 
the  lens  are  practically  parallel,  and  the  image  of  the  object  is 
at  the  principal  focus. 

Method  i.     Place  the  lens,  in  its  holder,  at  one  of  the  principal 


LABORATORY  COURSE  IN  PHYSICS  113 

divisions  of  the  meter  stick  and  place  the  cardboard  screen  behind 
it.  Go  to  the  back  of  the  room  and  point  the  lens  toward  an 
object  outside  the  window.  Move  the  screen  back  and  forth  until 
the  most  distinct  image  is  found.  Measure  the  distance  between 
the  lens  and  the  screen.  This  distance  is  the  principal  focal  length 
of  the  lens. 

Method  2.  If  the  sun  is  shining,  point  the  lens  at  the  sun  and 
move  the  screen  back  and  forth  until  you  find  the  smallest  and 
brightest  image  of  the  sun.  Measure  the  distance  between  the 
lens  and  the  screen.  This  distance  is  the  principal  focal  length. 

CONJUGATE  Foci 

The  meaning  of  conjugate  foci  may  be  illustrated  as  follows : 
if  an  object  is  placed  at  some  point  O  in  front  of  a  lens  and  its 
image  is  formed  on  a  screen  at  some  point  7  behind  the  lens,  then  O 
and  /  are  conjugate  foci,  because  if  the  object  is  placed  at  7  its 
"mage  will  be  formed  at  0.  There  is  an  infinite  number  of  pairs 
cf  conjugate  foci. 

Method.  Arrange  the  apparatus  as  shown  in  Fig.  43.  The 
object,  a  wire  netting  illuminated  from  behind  by  a  candle,  gas 
lamp,  or  electric  light,  is  at  one  end  of  the  meter  stick ;  a  white 
cardboard  screen,  to  receive  the  image,  is  near  the  other  end ;  and 
the  lens  is  between  the  two. 

Move  the  lens  back  and  forth  until  the  most  distinct  image  of 
the  netting  is  formed  on  the  screen.  Now  interchange  the  illu- 
minated wire  netting  and  the  cardboard  screen  without  moving 
the  lens.  Do  you  find  that  a  distinct  image  is  again  formed? 

Two  interchangeable  points  of  this  kind  are  called  conjugate 
foci  of  the  lens.  If  the  object  is  placed  at  the  first  point  the 
image  is  formed  at  the  second,  and  if  the  object  is  placed  at  the 
second  point,  the  image  is  formed  at  the  first. 

Move  the  screen  to  a  new  position  and  find  a  second  pair  of 
conjugate  foci. 


114  LABORATORY   COURSE  IN  PHYSICS 

To  find  the  principal  focus  from  the  conjugate  foci.  The  follow- 
ing equation  gives  the  relation  between  the  conjugate  foci  and  the 
principal  focus : 

_-L  +  -I_  =  .l 

Do     Di     F 

In  this  equation  Do  is  the  distance  of  the  object  from  the  lens, 
Di  is  the  distance  of  the  image  from  the  lens,  and  F  is  the  principal 
focal  length. 

Find  a  pair  of  conjugate  foci  and  measure  Do  and  Di,  put  these 
numbers  in  the  equation  above  and  calculate  F,  the  principal 
focal  length. 

FORM    OF   REPORT 

Principal  focal  length  (i)  =  cm. ;  (2)  =          cm.  • 

Conjugate  foci  (i)  =         cm.  and         cm. 
(2)  =         cm.  and         cm. 
Do  =       cm.     Di  =  cm.    F  =  cm. 


LABORATORY   COURSE   IN   PHYSICS 


Experiment  38.  Size  of  real  image  formed  by  a  converging  lens. 
To  show  that  the  size  of  the  image  is  to  the  size  of  the  object  as 
Di  is  to  Do. 

Meter  stick  and  supports.  Wire  netting. 

Lens.  Candle  or  lamp. 

White  cardboard  screen.  Meter  stick. 

Method.  Arrange  the  apparatus  as  shown  in  Fig.  43.  Place 
the  wire  netting  and  lens  a  certain  number  of  centimeters  apart, 
say  20,  and  move  the  screen  until  a  distinct  image  is  formed. 

We  wish  to  show  that  the  size  of  the  image  is  to  the  size  of  the 
object  as  Di  is  to  Do.  That  is,  if  the  distance  of  the  image  from 
the  lens  is  2,  3,  -J,  -J,  etc.,  times  the  distance  of  the  object  from  the 
lens,  then  the  size  of  the  image  will  be  2,  3,  -J,  ^,  etc.,  times  the  size 
of  the  object. 

Measure  Di,  the  distance  the  image  is  from  the  lens,  and  Do, 
the  distance  the  object  (the  wire  netting)  is  from  the  lens.  To 
find  the  size  of  the  image  measure  the  number  of  millimeters 
covered  by  10  squares  of  the  image  of  the  wire  netting.  To  find 
the  size  of  the  object,  measure  the  number  of  millimeters  covered 
by  10  squares  of  the  wire  netting  itself. 

Find:    gi.andS!zeofimaSe.     Are  they  equal? 
Do          Size  of  object 

Repeat  twice  with  the  netting  in  a  new  position  each  time. 
FORM    OF   REPORT 


i 

2 

3 

Distance  of  image  Di 

cm 

cm 

cm 

Distance  of  object  Do   

cm. 

cm. 

cm. 

Size  of  image   

mm. 

mm 

mm 

Size  of  object  .     . 

mm 

mm 

mm 

Di 

Do 
f  ize  of  image 

Size  of  object 

n6 


LABORATORY   COURSE   IN   PHYSICS 


Experiment  39.     Magnifying  power  of  a  lens  used  as  a  simple 
microscope. 

To  show  that  the  magnification  produced  by  a  converging  lens 
is  equal  to  Di  -r-  Do. 


FIG.  44.     Apparatus  used  to  measure  the  magnifying  power  of  a  simple  microscope. 

Converging  lens  (f.  =  2.5-5  cm.).  Scale,  mm. 

Black  screen  with  square  hole.  Meter  stick. 

(A  linen  tester  instead  of  the  above.) 

Method.  Place  a  mm.  scale  on  the  table  and  support  the  lens 
just  25  cm.  above  the  scale.  Beneath  the  lens  support  a  black 
screen  with  a  square  hole  about  10  mm.  on  each  side,  and  adjust 


LABORATORY  COURSE  IN  PHYSICS  117 

it  until  the  edges  of  the  hole  appear  distinct  when  viewed  through 
the  lens.  (A  linen  tester  has  lens  and  black  screen  with  square 
hole.) 

Look  through  the  lens  with  one  eye  and  look  at  the  scale  (with- 
out the  lens)  with  the  other  eye.  Find  the  size  (on  the  scale)  of 
the  image  of  the  hole.  Measure  the  distance  Do  of  the  object 
(the  black  screen)  from  the  lens. 

The  mm.  scale  is  placed  25  cm.  from  the  lens  (and  from  the  eye) 
because  this  is  the  distance  at  which  the  average  eye  sees  things 
of  this  size  most  distinctly. 

You  have  now : 

(1)  The  size  of  the  object  =  the  size  of  the  hole,  in  mm. 

(2)  The  size  of  the  image  =  the  size  of  the  image  of  the  hole,  in 
mm. 

(3)  The  distance  Do  of  the  object  =  the  distance  between  the 
square  hole  and  the  lens,  in  cm. 

(4)  The  distance  Di  of  the  image  =  25  cm. 

Find  the  magnification  =  size  of  image  -r-  size  of  object.  Is 
this  equal  to  Di  +  Do? 

FORM    OF   REPORT 

Size  of  Image  =  mm.  Di  =          cm. 

Size  of  Object  =  mm.  Do  =          cm. 

TV/T       •£     ,.1          Di  TIT       •£     «.i  Size  of  Image 

Magnification  =  —  =  Magnification  =  — .fe      = 

Do  Size  of  Object 

Exercise  30.     Light  Appliances. 

Examine  the  following  light  appliances  in  the  school:  mirror, 
camera,  projection  lantern,  stereoscope. 

Mirror.  Look  at  your  image  and  explain  why  it  is  reversed ;  that 
is,  why  your  right  hand  appears  to  be  your  left  in  the  image,  and 
vice  versa.  Explain  also  why  your  image  is  always  as  far  behind 
the  mirror  as  you  are  in  front.  Consult  page  254,  Physics  of  the 
Household. 


Il8  LABORATORY  COURSE  IN  PHYSICS 

Camera.  Measure  the  focal  length  of  the  camera  lens,  and 
calculate  where  the  image  will  be  formed  when  the  object  is  at 
different  distances  in  front  of  the  lens.  Consult  Experiment  37 
above.  The  plate  or  film  should  be  placed  at  these  calculated 
distances. 

Projection  Lantern.  Measure  the  focal  length  of  the  projection 
lens,  and  calculate  where  the  image  will  be  formed  when  the 
lantern  slide  is  at  different  distances  behind  the  lens.  Consult 
Experiment  37  above.  The  calculated  position  of  the  image  is 
where  the  screen  should  be  placed  to  get  the  best  image. 

Stereoscope.  Examine  this  and  explain  why  the  two  pictures 
appear  as  one,  and  why  the  object  appears  to  stand  out.  Consult 
page  268,  Physics  of  the  Household. 

Home  Exercise. 

Repeat  these  exercises  with  any  of  the  above  appliances  which 
you  have  in  your  home. 

Make  a  report  of  your  experiments. 


LABORATORY   COURSE  IN  PHYSICS  119 

Experiment  40.     The  astronomical  telescope. 

To  show  that  the  distance  between  the  lenses  in  an  astronomical 
telescope,  when  used  to  view  a  distant  object,  is  approximately 
equal  to  the  sum  of  the  principal  focal  lengths  of  the  lenses ;  and 
to  show  that  the  magnifying  power  is  equal  to  the  focal  length  of 
the  objective  divided  by  the  focal  length  of  the  eye-piece. 


FIG.  45.     Apparatus  used  to  illustrate  properties  of  an  astronomical  telescope, 

Lens  (f.  =  10-15  cm.).  Meter  stick  and  supports. 

Lens  (f.  =  2.5-5  cm-)- 


120  LABORATORY   COURSE   IN   PHYSICS 

Method.  Length  of  telescope.  Arrange  the  apparatus  as  shown 
in  Fig.  45.  Make  the  large  lens  used  in  Experiments  37  and  38 
the  objective  and  the  small  lens  used  in  Experiment  39  the  eye- 
piece. Go  to  the  side  of  the  room  farthest  from  the  window  and 
focus  this  rough  telescope  through  the  open  window  on  some  dis- 
tant object.  Measure  the  distance  between  the  lenses.  Is  it  equal 
to  the  sum  of  the  focal  lengths  of  the  lenses?  Find  these  focal 
lengths  again  if  necessary. 

Magnifying  power.  Draw  two  parallel  lines,  15  cm.  apart, 
on  the  blackboard  and  look  at  them  through  the  telescope  from 
the  other  side  of  the  room.  When  the  telescope  is  properly 
focused,  open  the  other  eye  and  direct  another  student  where  to 
draw  two  lines  on  the  board  which  coincide  with  the  image. 
Measure  the  distance  between  the  image  lines  and  divide  them  by 
the  distance  between  the  object  lines  to  find  the  magnification. 
Is  this  magnification  equal  to  the  focal  length  of  the  objective 
lens  divided  by  the  focal  length  of  the  eye-piece  lens? 

FORM    OF   REPORT 

Focal  length  of  objective  lens  =  .  . .  .  cm. 

Focal  length  of  eye-piece  lens  =  ....  cm. 

Distance  between  lenses  when  viewing  a  distant  object  =  .  . .  .  cm. 

Distance  between  image  lines  =  .  . .  .  cm. 

Distance  between  object  lines  =  .  . .  .  cm. 

Magnification  =  .  . .  . 
Focal  length  of  objective  -f-  Focal  length  of  eye-piece     =  .  . .  . 


LABORATORY  COURSE  IN  PHYSICS  1 21 

Experiment  41.     Refraction  and  dispersion  of  light  by  a  prism. 

To  show  how  a  ray  of  light  is  bent  or  refracted,  and  how  white 
light  is  spread  or  dispersed,  in  passing  through  a  prism. 


B  c 

FIG.  46.     Diagram  of  the  apparatus  used  to  show  how  light  is  bent  or  refracted. 

Glass  prism,  60°  angles.  Paper. 

Pins.  Candle. 

REFRACTION 

Method.  Place  the  prism  ABC  on  a  sheet  of  paper  and  draw  a 
line  along  each  edge.  Place  two  pins  DE,  Fig.  46,  in  a  line,  making 
an  angle  of  about  45°  with  one  edge.  With  a  ruler  sight  through 
the  prism  at  the  images  of  the  two  pins  and  draw  a  line  FG. 
Remove  the  prism  and  pins  and  draw  the  lines  DEH,  KFG,  and 
HK.  The  path  of  the  light  is  DEH  KFG.  At  what  two  points 
is  the  light  bent  or  refracted  ?  Make  a  drawing  of  this  in  your 
note  book. 

DISPERSION 

Method.  If  the  sun  is  shining,  support  a  prism  in  such  a  posi- 
tion, Fig.  47,  that  the  sunlight  falls  on  one  edge.  Catch  the  light 
which  passes  through  the  prism  on  a  piece  of  white  paper  placed 
on  the  table  or  on  the  floor.  Place  between  the  sunlight  and 
the  prism  a  piece  of  black  cardboard  with  a  slit  2  mm.  wide, 
Is  the  white  light  of  the  sun  spread  or  dispersed  into  a  colored 
band  (the  spectrum)?  Which  colors  do  you  recognize?  Which 
color  is  least  refracted,  that  is,  which  is  nearest  the  upper  angle  of 


122 


LABORATORY  COURSE  IN  PHYSICS 


the  prism?     Which   color  is  most   refracted,   that  is,   which   is 
nearest  the  base  of  the  prism  ? 

Make  a  drawing  in  your  note  book  showing  the  path  of  the  sun- 
light before  and  after  it 
passes  through  the  prism. 
Light  a  candle  and  look 
at  it  through  the  prism.  Is 
the  flame  colored?  Which 
colors  now  appear  the  least 
and  the  most  refracted? 

You  will  notice  that  these 
colors  are  just  opposite  to 
those  found  above.  The 
reason  is  that  the  eye  sees 
any  object  in  the  direction 
in  which  the  light  from  that 
object  enters  the  eye.  In 
this  case  the  white  light  is 
dispersed,  the  red  end  of 
the  spectrum  being  least 
refracted  and  the  blue  end 
most;  but  the  lines  along 
which  the  red  light  and 

Showing  how  the  prism  is  arranged    blue  light  enter  the  eye  are 

diverging,  and  if  they  are 
extended  back  they  cross  at  a  point  in  front  of  the  image ;  there- 
fore the  red  appears  to  be  the  most  refracted  and  the  blue  the 
least. 


FIG.  47. 
to  illustrate  the  dispersion  of  light. 


LABORATORY  COURSE  IN  PHYSICS  123 

SOUND 

Experiment  42.     Velocity  of  sound. 
To  measure  the  velocity  of  sound  in  air. 

Two  revolvers.  Blank  cartridges. 

Two  stop  watches.  Thermometer. 

Method.  On  a  calm  day,  divide  the  class  into  two  sections  and 
supply  each  section  with  a  revolver,  blank  cartridges,  and  a  stop 
watch.  Let  the  sections  stand  a  measured  distance  apart,  say 
|  mile.  If  the  wind  is  blowing  the  sections  should  stand  in  line 
with  the  wind,  if  possible.  Let  the  first  section  make  five  measure- 
ments of  the  time  it  takes  sound  to  travel  the  measured  distance  as 
follows :  One  member  has  the  stop  watch  and  when  ready  asks  a 
second  member  to  wave  a  handkerchief.  A  member  of  the  second 
section  then  fires  the  revolver  in  the  air  and  the  member  of  the 
first  section  with  the  stop  watch  measures  the  time  between 
seeing  the  flash  and  hearing  the  sound.  After  the  first  section 
has  made  five  measurements,  let  the  second  section  make  five 
in  the  same  way.  Take  the  average  of  the  ten  measurements 
as  the  time  it  takes  sound  to  travel  the  measured  distance,  and 
calculate  the  velocity  of  sound  per  second. 

This  method  gives  only  approximate  results,  but  furnishes  an 
excellent  illustration  of  the  velocity  of  sound  in  air.  The  velocity 
of  sound  in  air  is  1087  feet  (or  331  meters)  per  second  at  o°  C.,  and 
it  increases  about  2  feet  (or  0.6  meter)  per  second  for  each  degree 
centigrade  increase  in  temperature. 

FORM   OF   REPORT 

Temperature  of  air                =  .  . .  .  °C 
Distance  between  divisions  =  .  . .  . 
Average  time                         =  .  . .  .  sec. 
Velocity  of  sound  per  sec.     = 


124 


LABORATORY  COURSE  IN  PHYSICS 


LABORATORY  COURSE  IN  PHYSICS  125 

Experiment  43.     Number  of  vibrations  of  a  tuning  fork. 

To  find  the  number  of  vibrations  a  tuning  fork  makes  per  second. 

Tuning  fork.  Paint  (whiting  and  alcohol). 

Recording  apparatus.  Sponge. 

Watch. 

One  vibration  of  a  tuning  fork  consists  of  a  complete  to  and  fro 
motion;  we  wish  to  determine  how  many  of  these  a  fork  makes 
per  second.  The  number  is  so  great  that  it  cannot  be  determined 
by  the  unaided  eye  and  it  is  necessary  to  employ  some  such  ap- 
pliance as  is  illustrated  in  Fig.  48.  This  consists  essentially  of : 
a  pendulum  with  a  light  stylus  on  the  end ;  the  fork  with  a  light 
stylus  on  one  prong ;  and  a  glass  plate  which  can  be  moved  under 
the  pendulum  and  the  fork. 

Method.  Find  the  time  it  takes  the  pendulum  to  make  50 
vibrations  and  calculate  the  number  of  vibrations  per  second  (a 
vibration  is  a  complete  to-and-fro  motion).  Make  three  deter- 
minations and  take  the  average. 

Cover  one  side  of  the  glass  plate  with  a  mixture  of  whiting  and 
alcohol  by  means  of  a  small  sponge. 

Place  the  plate  under  the  pendulum  and  fork  and  adjust  these 
so  that  the  styluses  touch  the  glass  lightly. 

Start   the  fork  and   the  pendulum  vibrating   and   move    the 
plate  lengthwise.     If  your  adjustments  are  correct  you  will  ob- 
tain a  trace  resem-  \  /  \ 
bling  that  shown  in    ~fc^™^\~^™™^         -A~~ 

Fig.  49.  FIG.  49.    Illustrating  the  traces  of  the  fork  and  of  the 

Calculate  the   pendulum, 
number  of  vibrations  of  the  fork  per  second  as  follows: 

The  marks  A  and  C  or  B  and  D  each  represent  those  made  at 
the  beginning  and  end  of  one  vibration  of  the  pendulum.  Count 
the  number  of  vibrations  (hills  on  one  side  only)  of  the  fork  be- 
tween three  such  spaces  as  A  to  C  or  B  to  Z>,  estimating  each  to 
tenths  of  a  vibration.  Multiply  this  by  the  number  of  vibrations 


126 


LABORATORY  COURSE  IN  PHYSICS 


the  pendulum  makes  in  one  second.     The  product  is  the  number 
of  vibrations  the  fork  makes  per  second. 


FORM    OF   REPORT 


i 

2 

3 

AVERAGE 

Time  of  50  vibrations  of  the  pendulum  = 
Vibrations  of  the  fork  in  one  pendulum 
vibration  — 

Vibrations  of  pendulum  per  second    .  = 
Vibrations  of  fork  per  second    .     .     .  = 

LABORATORY   COURSE  IN  PHYSICS 


127 


Experiment  44.     Wave  length  of  sound. 

To  measure  the  length  of  the  sound  waves  produced  by  a  tuning 
fork  and  to  measure  the  velocity  of  sound  in  air  indirectly. 


FIG.  50.     Apparatus  used  to  measure  the  length  of  the  sound  waves  produced  by  a 
tuning  fork  and  to  measure  the  velocity  of  sound  indirectly. 


Tuning  fork  (n  =  512). 
Hydrometer  jar  18"  deep. 
Resonance  tube  20"  long. 


Meter  stick. 

Two  rubber  bands. 


WAVE  LENGTH 

Method.  Fill  the  hydrometer  jar  with  water  and  place  the 
resonance  tube  in  it.  Sound  the  tuning  fork  by  striking  it  on  a 
large  flat  cork  or  on  a  piece  of  heavy  rubber  tubing,  and  hold  it 
over  the  resonance  tube.  Raise  the  resonance  tube  slowly  and  find 
the  length  of  air  column  which  gives  the  loudest  sound.  Mark 
this  length  by  means  of  a  rubber  band.  Repeat  until  you  are  sure 


128  LABORATORY   COURSE  IN  PHYSICS 

you  have  the  exact  length.  Raise  the  resonance  tube  and  find  a 
longer  air  column  which  gives  a  loud  sound.  Mark  this  with 
a  rubber  band.  Repeat  until  you  have  the  exact  length. 

The  length  of  the  short  air  column  is  approximately  equal  to 
one  fourth  the  wave  length  of  the  sound.  The  difference  between 
the  lengths  of  the  two  air  columns  is  equal  to  one  half  the  wave 
length  of  the  sound  given  out  by  the  fork.  Measure  the  distance 
between  the  two  rubber  bands  and  multiply  it  by  2  to  obtain  the 
length  of  the  sound  wave. 

VELOCITY  OF  SOUND 

You  have  found  the  length  of  each  sound  wave  given  out  by 
the  fork.  Now  since  the  fork  makes  512  complete  vibrations  per 
second,  it  sends  out  512  waves  each  second,  and  since  each  wave 
moves  continuously  at  the  same  velocity,  the  product,  512  X  wave 
length,  is  equal  to  the  distance  the  sound  moves  in  air  in  one 
second,  that  is,  it  is  equal  to  the  velocity  of  sound  in  air  per  second. 

Multiply  the  wave  length  found  above  by  512  to  find  the  ve- 
locity of  sound  per  second  at  the  temperature  of  the  laboratory. 

FORM    OF    REPORT 

Distance  between  rubber  bands  =  .  . .  .  cm. 
Wave  length  =  .  . .  .  cm. 

Velocity  of  sound  per  sec.  =  .  . .  .  cm. 

Temperature  =  .  . .  .  °C. 


LABORATORY  COURSE  IN  PHYSICS 


129 


Experiment  45.     Vibrating  strings. 

To  show  that  the  vibration  frequency  varies  inversely  as  the 
length  of  the  wire,  and  that  the  notes  of  an  octave  are  produced  by 
lengths  of  wire  which  are  in  the  ratio  of  i,  f ,  f,  f,  f,  f,  T8g-,  J. 


FIG.  51.     A  simple  sonometer. 


Sonometer. 
Sonometer  wire. 


Meter  stick. 
Chalk. 


In  your  class  work  you  have  learned  that  the  pitch  of  a  note 
depends  upon  the  number  of  vibrations  per  second  of  the  instru- 
ment producing  it;  for  example,  the  number  of  vibrations  per 
second  required  to  produce  a  note  one  octave  higher  than  a  given 
note  is  twice  as  great  as  the  number  required  to  produce  the  given 
note. 

Method.  Vibration  frequency  varies  inversely  as  the  length. 
Stretch  a  piano  wire  on  a  sonometer  and  adjust  the  bridge  until 
the  wire  is  a  definite  length  (between  80  cm.  and  100  cm.).  Mark 
on  the  sonometer  lengths  \  and  J  of  the  length  of  the  string. 

Sound  the  note,  then  move  the  bridge  until  the  length  of  the 
wire  is  \  and  sound  it  again.  Is  the  second  note  one  octave  higher 
than  the  first  note  ? 

Move  the  bridge  until  the  length  of  the  wire  sounded  is  J  the 
length  of  the  first,  that  is,  \  the  length  of  the  second.  Is  the  third 
note  one  octave  higher  than  the  second?  Does  the  vibration 
frequency  vary  inversely  as  the  length  of  the  wire  ? 


130  LABORATORY  COURSE  IN  PHYSICS 

The  notes  of  an  octave.  Stretch  the  wire  and  adjust  the  bridge 
until  the  length  of  the  wire  is  just  90  cm.  On  the  board  of  the 
sonometer  mark  lengths  equal  to  i,  f ,  f ,  f ,  f ,  f ,  T85-,  and  \  of  the 
90  cm.  Sound  the  wire  at  the  90  cm.  length  and  then  move  the 
bridge  to  each  of  the  shorter  lengths  in  turn  and  sound  the  wire. 
Are  the  notes  produced  those  of  an  octave  ? 


LABORATORY   COURSE   IN   PHYSICS 


ADVANCED   MECHANICS 
Experiment  46.     The  parallelogram  law. 
To  illustrate  the  parallelogram  law. 


FIG.  52.     The  apparatus  used  to  illustrate  the  parallelogram  law. 


Three  spring  balances. 
Large  sheet  of  paper. 


Ruler. 

Three  small  clamps. 


The  parallelogram  law  of  forces  is :  //  two  forces  acting  at  an 
angle  upon  a  point  are  represented  in  direction  and  amount  by  straight 
lines,  the  resultant  of  the  two  forces  is  exactly  represented  in  direction 
and  amount  by  the  diagonal  of  the  parallelogram  of  which  the  lines 
are  the  sides.  The  equilibrant  is  equal  to  the  resultant,  but  is  in  the 
opposite  direction. 

Method.  Attach  a  stout  cord  to  the  ring  of  each  balance.  Con- 
nect the  hooks  of  two  balances  by  means  of  a  piece  of  strong  fish 
line  about  30  cm.  long.  Attach  the  hook  of  the  third  to  the  middle 
of  this  line  by  means  of  a  piece  of  fish  line  about  15  cm.  long. 


132  LABORATORY  COURSE  IN  PHYSICS 

Attach  the  balances  to  clamps  so  placed  that  the  cords  are  over  a 
piece  of  paper  or  a  page  of  your  notebook  in  the  relationship 
shown  in  Fig.  52,  having  one  balance  at  C,  one  at  B,  and  one  at  A. 

Pull  the  balance  A  in  order  to  stretch  each  balance.  Mark 
carefully  the  point  O  and  draw  a  short  line  under  each  cord  in  the 
manner  illustrated  in  the  middle  figure.  Mark  beside  each  line  the 
number  of  ounces  (or  pounds)  pull  on  the  corresponding  balance. 

Remove  the  balances  and  draw  the  lines  OC,  OB,  and  OA,  mak- 
ing their  lengths  equal  to  the  number  of  ounces  (or  pounds)  pull 
on  the  corresponding  balances,  according  to  any  convenient  scale 
(}  in.  =  i  ounce,  etc.). 

On  the  lines  OC  and  OB  construct  a  parallelogram.  Then 
measure  the  length  of  the  diagonal  OR  and  calculate  the  force  it 
represents.  This  is  the  resultant.  Is  it  equal  to  the  equilibrant 
represented  by  OA  ?  Is  the  resultant  represented  in  direction  and 
amount  by  the  diagonal  of  the  parallelogram  ? 


LABORATORY  COURSE  IN  PHYSICS  133 

Experiment  47.     Efficiency  of  a  machine. 

To  determine  the  efficiency  of  a  commercial  block  and  tackle. 

Block  and  tackle.  Spring  balance. 

Weights.  Yard  stick. 

A  machine  is  any  contrivance  by  means  of  which  a  force  applied 
at  one  point  exerts  a  pressure  or  a  pul  at  another  point. 

The  efficiency  of  any  machine  is  the  ratio  of  the  work  done  by  the 
machine  to  the  work  put  into  it,  that  is, 

output 

Efficiency  =  7-^  —  • 
input 

The  law  of  machines  is :  //  there  is  no  friction,  the  weight  times 
the  distance  the  weight  moves  (output)  is  equal  to  the  force  times  the 
distance  the  force  moves  (input). 

In  all  actual  machines  there  is  friction,  that  is,  a  force  which 
resists  motion.  This  friction  is  due  to  the  roughness  of  the  bear- 
ings, the  stiffness  of  belts  or  ropes,  and  to  other  causes.  In  an  actual 
machine,  then,  force  is  required  to  overcome  friction  and  therefore 
the  input  is  always  greater  than  the  output.  In  many  machines 
work  also  must  be  done  to  move  parts  of  the  machine  (for  example, 
to  lift  the  lower  block  of  this  block  and  tackle).  This  is  classed  as 
useless  work,  since  it  helps  to  make  the  input  greater  than  the 
output. 

Method.  Support  the  upper  block  in  a  suitable  manner  and 
attach  a  weight  of  10  Ib.  to  the  lower  block.  Find  the  force  in 
pounds  required  to  raise  the  weight  slowly. 

Lower  the  weight  until  it  is  just  touching  the  floor ;  mark  the 
position  of  the  spring  balance  and  measure  the  distance  the  force 
(the  balance)  moves  to  raise  the  weight  i  foot. 

Calculate  the  work  in  foot  pounds  done  by  the  machine  in 
raising  the  weight  i  foot  =  weight  X  distance  weight  moves  = 
10  X  i  =  10  foot  pounds  =  output. 

Calculate  the  work  in  foot  pounds  put  into  the  machine  = 


134 


LABORATORY  COURSE  IN   PHYSICS 


force  X  distance  force  moves  in  raising  weight  i  foot  =  input. 
Calculate  the  efficiency  =  output  -5-  input. 

Attach  a  weight  of  20  Ib.  to  the  lower  block  and  find  the  force 
in  pounds  required  to  raise  it  slowly.  Calculate  the  output,  input, 
and  efficiency. 

Repeat  with  a  weight  of  30  Ib. 

Does  the  efficiency  of  the  machine  increase  with  the  weight? 

FORM    OF   REPORT 


WEIGHT 

OUTPUT 

FORCE 

INPUT 

EFFICIENCY 

I 

Ib. 

ft.  Ib. 

Ib. 

ft.  Ib. 

% 

2 

Ib. 

ft.  Ib. 

Ib. 

ft.  Ib. 

% 

3 

Ib. 

ft.  Ib. 

Ib. 

ft.  Ib. 

% 

If  the  block  and  tackle  is  not  available  use  the  small  laboratory 
pulleys  (see  Fig.  9),  and  use  weights  of  200  g.,  400  g.,  and  600  g. 
Measure  the  input  and  output  in  gram  centimeters. 


LABORATORY  COURSE  IN  PHYSICS  135 

Experiment  48.     Accelerated  motion. 

To  show  that  the  space  a  body  falls  varies  as  the  square  of  the 
time  and  that  the  velocity  of  fall  is  independent  of  the  weight  of 
the  body. 

To  find  the  velocity  of  a  projectile. 

Pebbles.  Watch. 

The  formula  for  finding  the  space  a  body  falls  from  rest  is 
s  =  \  gt2-  Where  5  is  the  distance  the  body  falls,  g  the  constant 
of  acceleration,  and  /  is  the  time  in  seconds.  If  we  use  32  ft.  per 
second  as  the  constant  of  acceleration,  the  distance  a  body  falls 
in  i  second  is  5  =  \  X  32  X  i2  =  16  ft. ;  the  distance  it  falls  in 
2  seconds  is  s  =  f  X  32  X  22  =  64  ft. 

FALLING  BODIES 

Method.  Let  the  students  go  out-of-doors  and  measure  from 
the  ground  a  distance  of  16  feet  up  the  side  of  the  building  to  a 
window  or  a  balcony.  Let  one  student  hold  his  hand  at  this 
height  and  let  pebbles  fall  one  at  a  time  at  a  given  signal.  Let 
another  student  use  a  watch  with  well-marked  seconds  and  an- 
nounce at  the  end  of  successive  seconds,  "  one,  two,  three,  go,  one, 
two."  At  the  word  "  go  "  let  the  first  student  drop  a  pebble  and 
let  both  notice  whether  the  pebble  strikes  the  ground  in  one  second. 
Make  a  number  of  trials. 

Does  the  body  fall  16  feet  in  one  second? 

Let  the  first  student  hold  weights  of  i  and  2  Ib.  side  by  side 
and  let  them  fall.  Does  the  velocity  depend  upon  the  weight? 

Measure  up  the  side  of  the  building  36  feet  and  repeat  the  ex- 
periments. Does  the  body  fall  36  feet  in  i-J-  seconds  ? 

Measure  up  the  side  of  the  building  a  distance  of  64  feet  above 
the  ground  and  repeat  the  experiments.  Does  the  body  fall  64 
feet  in  2  seconds  ?  Is  the  space  a  body  falls  from  rest  proportional 
to  the  square  of  the  time? 


136  LABORATORY   COURSE  IN  PHYSICS 

Drop  weights  of  i  and  2  Ib.  from  this  height. 
Does  the  velocity  of  fall  depend  upon  the  weight? 

PROJECTILES 

The  velocity  of  a  body  thrown  vertically  upwards  decreases 
32  feet  per  second  each  second  it  is  rising ;  if  then  a  body  is  thrown 
vertically  upward  and  rises  for  2  seconds  its  velocity  at  the  start 
was  V  —  gt  =  32  X  2  or  64  feet  per  second;  if  it  rose  3  seconds 
its  velocity  at  the  start  was  7  =  ^=32X3=96  feet  per 
second,  and  so  on. 

Let  one  student  at  a  time  throw  a  stone  vertically  upward  and 
let  a  second  student  take  the  time  in  seconds  from  the  instant  the 
stone  leaves  the  hand  until  it  strikes  the  ground.  Half  of  this  is 
the  time  in  seconds  the  stone  rose.  Calculate  from  this  the  velocity 
in  feet  per  second  of  the  stone  when  it  left  the  hand. 


LABORATORY   COURSE  IN  PHYSICS 


137 


Experiment  49.     Laws  of  the  pendulum. 

To  show  that  the  time  of  swing  of  a  pendulum  is  independent 
of  the  amplitude,  for  small  amplitudes ;  and  that  the  time  of  swing 
varies  as  the  square  root  of  the  length  of  the  pendulum. 


Pendulum. 


Watch. 


Method.  Time  of  swing  independent  of  the  amplitude,  for  small 
amplitudes.  Make  a  pendulum  about  3  ft.  long  and  start  it  swing- 
ing through  an  arc  of  about  6  in.  With  a  watch  take  the  time  of 
100  swings.  Start  it  swinging  through  an  arc  of  i  foot  and  take 
the  time  of  100  swings.  Is  the  time  of  swing  independent  of  the 
amplitude  ? 

Time  of  swing  varies  with  the  length.  Attach  a  metal  sphere 
(about  i  in.  diam.)  to  a  fine  wire  and  make  the  length  of  the 
pendulum  (from  the  point  of  support  to  the  center  of  the  bob) 
exactly  ij  foot.  Find  the  time  of  100  swings  and  calculate  the 
time  of  one  swing. 

Set  up  a  pendulum  exactly  6  feet  long.  Find  the  time  of  100 
swings  and  calculate  the  time  of  one  swing. 

The  6  foot  pendulum  is  4  times  as  long  as  the  i  J  foot  pendulum ; 
is  its  time  of  swing  ^4  or  2  times  that  of  the  ij  foot  pendulum, 
that  is,  does  the  time  of  swing  vary  directly  as  the  square  root 
of  the  length  of  the  pendulum? 

FORM    OF   REPORT 


ioo  SWINGS 

i  SWING 

Amplitude  6  in.,  time           

Amplitude  12  in    time                        .... 

Pendulum  i  ^  f  t    long  time 

Pendulum.  6  ft  long    time 

138  LABORATORY  COURSE  IN  PHYSICS 

APPENDIX 
TABLE   OF   DENSITIES 

Alcohol  ("  absolute  ")       0.8  Lead  ......  11.4 

Aluminium   .     .    .'....-.     2.65  Limestone  ....       2.6-2.8 

Brass  ......       8.5  Marble  .....       2.5-2.8 

Cork    ......      0.2  Mercury      ....  13.6 

Copper     .....       8.5-8.9          Milk  ......       1.03-1.033 

Gasoline  .....       0.68-0.72      Oak  wood  ....       0.7-0.9 

Glass  (Flint)      .     .     .       3.0-5.9          Pine  wood  ....      0.5 

Glass   ......       2.5-2.7          Platinum    ....  21.5 

Granite     .....       2.5-2.9          Sandstone  ....       1.9-2.5 

Gold    ......     19.3  Sea  water   ....       1.03 

Iron     ......       7-i~7-9          Sulphur.     ...     .       2.0 

Kerosene  .....      0.80  Vinegar  .....       1.01-1.08 

The  density  of  air  at  20°  C.  or  68°  F.  and  at  i  atmosphere  pressure 
(76  cm.)  is  1.205  g-  Per  ^ter  or  .0012  g.  per  cc. 


Coefficients  of  Linear  Expansion  of  Solids 

Brass      .......  0000189      Steel    ........  oooon 

Copper  .......  0000167 

Table  of  Specific  Heals 

Aluminium    .......  220      Iron      .........  no 

Brass    .........  090      Lead     .........  03  1 

Copper      .........  094      Mercury   ...     .....  033 

Resistance  of  Wire  per  ic&ofeet 
No.  30  Brown  and  Sharp  Gauge 

Copper  German-silver  Iron  (annealed) 

18%  Nickel 
105.1  ohms  1892  ohms  909-5  ohms 


LABORATORY  COURSE  IN  PHYSICS  139 

APPARATUS     FOR     LYNDE'S     LABORATORY     COURSE     IN 
PHYSICS   OF   THE   HOUSEHOLD 

EXPERIMENT  APPARATUS  APPROXIMATE 

COST 

MECHANICS 

1.  Yardstick  .25 
Lever  support  .50 
Iron  weight  with  ring,  2  Ib.  .75 
Iron  weights  with  ring,  i  Ib.,  2  @  .75  1.50 
Meter  stick  .30 

2.  Spring  balance,  2000  g.,  64  oz.  .55 
Block  of  wood  8"  X  A"  X  3!"  -3<> 
Laboratory  support,  tripod  base,  leg  12.5  cm.  .50 
Rod  80  cm.,  13  mm.  .60 
Clamp,  right  angle  .45 
Clamp  with  15  cm.  rod  .35 

3.  Single  pulleys,  4  @  .20  .80 

4.  Gallon  to  \  pint,  5  pieces  1.25 
Pail,  a  cube  6"  X  6"  X  6"  .75 
Balance,  Ib.,  with  flat  platforms,  and  side  beam 

o  to  16  oz.,  5  weights,  i  Ib.  3.75 

or  Standard  family  scale  1.75 

5.  Liter  measure  .50 
Balance  (gram)  12.75 
Weights  in  holder,  500  to  10  g.  1.65 

6.  Pail,  12  quart  -65 
Pails,  3  quart,  4  @  .20  .80 
Overflow  pail  with  spout  and  handle, 

81"  X  si"  X  sl"  deep  .75 

7.  Aluminium  cylinder,  with  hook  -45 
Graduated  cylinder,  100  cc.  -7° 

8.  Apparatus  listed  above 

9.  Specific  gravity  bottle,  50  cc.  i-io 
Hydrometer,  universal  i-45 
Hydrometer  jar  18"  X  3"  I-I° 

10.         Barometer  tube,  ordinary  tubing  f " 

sealed  at  one  end,  120  cm.  long  .4° 


140  LABORATORY  COURSE  IN  PHYSICS 

Same,  tubing  \  in.,  100  cm.  long  .25 

Evaporating  dish,  3  in.  dia.  .15 

Evaporating  dish,  4  in.  dia.  .30 

Mercury,  2  Ib.  @  1.50  3.00 

Funnels,  \\"  dia.,  2  @  .20  .40 

Siphon,  2  pieces  glass  tubing  f ",  30"  long,  @  .10  .20 
Heavy  rubber  tubing  to  fit  glass  tubes 

above,  18"  .30 

11.  Boyle's  Law  tubes  unfilled  .30 
Sealing  wax,  i  stick  .15 

HEAT 

12.  Tumblers,  2  @  .10  .20 
Thermometers  (—  10°  to  no0  C. 

and  —  17°  to  220°  F.),  2  @  1.25  2.50 

Boiler  hypsometer  3.00 

or  Boiler  (sirup  can,  i  gal.)  .25 
Stopper,  2  hole,  glass  tube  elbow, 

to  fit  sirup  can  .15 

Tripod,  5  in.  .25 

Bunsen  burner  .25 

Rubber  tubing,  T\",  2  feet  .20 

13.  Expansion  apparatus  3.00 

14.  Flask,  1000  c.c.  .60 
One  hole  rubber  stoppers,  2,  to  fit  flask  above  .10 
Glass  elbow,  rubber  tube  3  in.  and  clip  .25 

15.  Flatiron,  about  4  Ib.  .30 

1 6.  Cloth  strainer  .05 

17.  Apparatus  listed  above 

18.  Calorimeter  2.60 
Lead  shot,  2  Ib.  @  .15  .30 
Small  iron  nails,  i  Ib.  .10 
Aluminium  pellets,  |  Ib.  .70 
or  Sheet  lead,  f",  £  sq.  foot  .65 
Aluminium  weight  i.io 

19.  Apparatus  listed  above 

20.  Water  trap  .25 


LABORATORY  COURSE  IN  PHYSICS  141 

ELECTRICITY  AND  MAGNETISM 

21.  Student's  demonstration  battery  1.33 
Simple  galvanometer  1.25 
Compass  1.60 

22.  U  magnets,  2  @  .30  .60 
Carton  iron  filings  .10 
Soft  iron  bar  6"  X  \"  .10 
Pliers,  4^  in.  .40 
Bar  magnet  .20 

23.  Pane  of  glass,  15"  X  15"  .25 
Compass,  10  mm.  .15 
Filings  sifter  .10 

24.  Dry  cells,  2  @  .30  .60 
Soft  iron  horseshoe  .10 

25.  Electric  bell  -45 
Push  button  .TO 
Telegraph  sounder  and  key,  2  5.50 

26.  Demonstration  motor  with  electromagnet  3.50 

27.  Lead  elements,  12.5  X  2  cm.,  2  @  .05  .10 

28.  Wheatstone  bridge  3.00 
Resistance  box  7-5° 
D'Arsonval  galvanometer  3.00 
Contact  key  -75 

29.  Voltmeter  and  ammeter  on  stand  33 .00 
Electric  immersion  heater,  no  volts  3.75 

30.  Apparatus  listed  above 

31.  Apparatus  listed  above 

32.  Magneto  5.50 
Dynamo,  hand  power  35-°° 
Lamp  and  receptacle  for  dynamo  -5° 
Induction  coil  (demonstration)  6.00 
Nails,  5  inch,  4  -io 

33.  Motor,  A  h.p.  23.00 
Speed  counter  i.io 
Large  clamp,  6  in.  .65 


142  LABORATORY  COURSE  IN  PHYSICS 

LIGHT 

34.  Bunsen  photometer,  student's  i.oo 
Kerosene  lamp  .25 
Electric  light  receptacle  .25 
Attaching  plug  .40 
#18  Lamp  cord,  10  feet  .60 
Carbon  lamp  16  c.p.,  no  v.  .30 
Tungsten  lamp  40  w.,  no  v.  .85 

35.  Thin  mirror  4"  X  4"  .10 
Black  pins,  i  paper  .05 
Protractor,  brass,  3!"  .15 
Ruler,  i  foot  .10 

36.  Plate  glass,  parallel  sides  .20 
Drawing  compass  .15 

37.  Lens  holders,  2  @  .10  .20 
Lens,  8  in.  focus  .30 
Screen  supports,  2  @  .10  .20 
Screens,  2  @  .05  .10 
Wire  gauze  screen  .10 

38.  Apparatus  listed  above 

39.  Linen  tester  .35 

40.  Apparatus  listed  above 

41.  Glass  prism  i.io 

SOUND 

42.  Revolvers,  2  @  3.00  6.00 
Stop  watches,  2  @  7.50  i5-°° 
Boxes  blank  cartridges,  2  @  .50  i.oo 

43.  Vibratograph  3 -60 
Tuning  fork  for  above  1.3  5 
Extra  plates,  3  @  .10  -3° 
Whiting  and  sponge  .15 

44.  Tuning  fork  512  .09 
Resonance  tube,  20"  X  i|"  -5° 
Rubber  bands,  6  .05 

45.  Simple  sonometer  i-35 
Sonometer  wires,  set  of  4  .25 


LABORATORY  COURSE  IN  PHYSICS  143 

ADVANCED  MECHANICS 

46.  Small  clamps,  3  @  .25  .75 
Spring  balances,  2000  g.,  64  oz.,  2  at  .55  i.io 

47.  Apparatus  listed  above 

48.  Apparatus  listed  above 

49.  Pendulum  bobs,  i  in.,  2  .20 

GENERAL  SUPPLIES 

Sulphuric  acid,  i  Ib.  .35 

Table  salt,  3  Ib.  bag  .15 

Potassium  hydroxide  sticks,  i  Ib.  1.25 

Copper  sulphate,  3  Ib.  .90 

Kerosene,  i  gal.  .15 

Whiting,  4  oz.  .10 

Candles,  5  in.  long,  i  doz.  .20 

Fish  line,  i  card,  25  yards,  best  .20 

Linen  thread,  spool  .15 

Wire  #22  c.c.  copper,  i  Ib.  1.30 

Wire  #30  bare  G.  S.,  4  oz.  .60 

Wire  #30  bare  iron,  4  oz.  .25 

Sewing  needles,  i^  in.,  i  package  .10 

APPARATUS   FOR    STUDENT'S  PRIVATE  LABORATORY 

APPARATUS  APPROXIMATE 

COST 
MECHANICS 

Laboratory  support  tripod,  leg  12.5  .50 

Rod,  80  cm.,  13  mm.  .60 

Clamp  with  15  cm.  rod  -35 

Clamp,  right  angle  -45 

Yard  stick  .25 

Meter  stick  -3r 

Single  pulleys,  4  @  .20  .80 

Overflow  pail,  8|"  X  $¥'  X  5^"  deep  .75 

Pail,  3  quart  .15 

Spring  balance,  2000  g.,  64  oz.  .55 

Barometer  tube  complete  with  cup  and  pipette           .50 


144  LABORATORY  COURSE  IN  PHYSICS 

Siphon,  2  pieces  glass  tubing  f"  X  30"  .20 

Rubber  tubing  to  fit  glass  tubes  above,  i|  ft.  .30 

Boyle's  Law  tube  unfilled  .30 

Mercury,  f  Ib.  2.25 

Sealing  wax,  i  stick  .15 

HEAT 

Pails,  3  quart,  3  @  .15  .45 
Thermometer  C.  and  F.  (—  10°  to  110°  C.  and 

-    17°  tO  220°  F.)  I.2S 

Thermometer,  common  tin  back,  10°  to  220°  F.  .25 

Boiler,  i  gal.  sirup  can  .25 
Stopper,  rubber,  i  one-hole, 

i  two-hole  to  fit  boiler  .10 

Glass  tube  elbow  .05 

Tumbler  .10 

Tripod,  5  in.  .25 

Bunsen  burner  .25 

Rubber  tubing,  &  in.,  3  feet  .25 

Flask,  1000  c.c.  capacity  .60 

Rubber  stopper,  one-hole  to  fit  flask  .05 

Pinchcock  .10 

ELECTRICITY  AND  MAGNETISM 

Demonstration  cell  complete  1.3  5 

Lead  elements,  2  extra  .10 

Simple  galvanometer  1.25 

Compass,  16  mm.  .20 

U  magnets,  2  @  30  .60 

Bar  magnet  .20 

Carton  iron  filings  -io 

Soft  iron  bar,  6"  X  \"  -io 

Soft  iron  horseshoe  core  -io 

Dry  cells,  2  .60 

Pane  of  glass,  15"  X  15"  -25 

Electric  bell  45 

Push  button  .10 


LABORATORY  COURSE  IN  PHYSICS  145 

Telegraph  sounder  and  key  2.75 

Demonstration  motor  complete  3.50 

Miniature  lamp,  2-5  v.  .30 

Receptacle  .15 

LIGHT  AND  SOUND 

Thin  mirror,  4"  X  4"  .10 

Black  pins,  glass  heads  .05 

Plate  glass,  parallel  sides  .20 

Protractor  .15 

Optical  bench  support  blocks  .15 

Lens  support  .10 

Screen  supports,  2  @  .10  .20 

Bunsen  screen  .15 

Wire  gauze  screen  .10 

Candle  holder  .10 

Candles,  i  Ib.  .20 

Lens,  8  in.  focus  .30 

Linen  tester  .35 

Screen  .05 

Prism  1. 10 

Sonometer  wires,  set  of  4  .25 

Tuning  fork  A  .15 

Tuning  fork  C  .15 

ADVANCED  MECHANICS 

Pendulum  bob,  i  in.  .10 


SUPPLIES 

Sulphuric  acid,  i  oz.  .35 

Potassium  hydroxide  sticks,  i  oz.  .20 

Copper  sulphate,  8  oz.  .15 

Copper  wire  c.c.  #22,  4  oz.  .40 

Sewing  needles,  i£",  i  package  .10 


146  LABORATORY  COURSE  IN  PHYSICS 

FIRMS 

The   apparatus   for  Lynde's  Laboratory   Course   in   Physics   of  the 
Household  can  be  purchased  from  the  following  firms : 

UNITED  STATES 

Central  Scientific  Co.,  412  Orleans  St.,  Chicago,  111. 
Chicago  Apparatus  Co.,  32  South  Clinton  St.,  Chicago,  111. 
Wm.  Gaertner  &  Co.,  5345  Lake  Park  Ave.,  Chicago,  111. 
L.  E.  Knott  Apparatus  Co.,  Boston,  Mass. 
Kny  Sheerer  Co.,  225  Fourth  Ave.,  New  York,  N.Y. 
Standard  Scientific  Co.,  147  Waverly  Place,  New  York,  N.Y. 
C.  H.  Stoelting  &  Co.,  31  Randolph  St.,  Chicago,  111. 

CANADA 

George  M.  Hendry  &  Co.,  Ltd.,  215  Victoria  St.,  Toronto,  Ont. 
McKay  School  Equipment  Co.,  Ltd.,  615  Yonge  St.,  Toronto,  Ont. 
Toronto  School  Supply  Co.,  Ltd.,  210  Victoria  St.,  Toronto,  Ont. 

GREAT  BRITAIN 

Baird  and  Tatlock,  Ltd.,  Hatton  Garden,  London,  England. 
W.  &  J.  George,  Ltd.,  157  Great  Charles  St.,  Birmingham,  Eng. 
Philip  Harris  &  Co.,  Ltd.,  Edmund  St.,  Birmingham,  Eng. 


Printed  in  the  United  States  of  America. 


